diff --git a/storm_analysis/psf_fft/fft_fit.c b/storm_analysis/psf_fft/fft_fit.c
index 779cfe62..e20a13c3 100644
--- a/storm_analysis/psf_fft/fft_fit.c
+++ b/storm_analysis/psf_fft/fft_fit.c
@@ -98,7 +98,8 @@ void ftFitCalcJH3D(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = rqei*height*(dx[l]);
     jt[2] = rqei*height*(dy[l]);
     jt[3] = rqei*height*(dz[l]);
-    jt[4] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = rqei/((double)fit_data->bg_counts[k]);
 
     /* Calculate jacobian. */
     t1 = 2.0*(1.0 - xi/fi);
diff --git a/storm_analysis/pupilfn/pupil_fit.c b/storm_analysis/pupilfn/pupil_fit.c
index 1a163e40..b9bf5836 100644
--- a/storm_analysis/pupilfn/pupil_fit.c
+++ b/storm_analysis/pupilfn/pupil_fit.c
@@ -104,7 +104,8 @@ void pfitCalcJH3D(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = rqei*2.0*height*(psf_r[l]*dx_r[l]+psf_c[l]*dx_c[l]);
     jt[2] = rqei*2.0*height*(psf_r[l]*dy_r[l]+psf_c[l]*dy_c[l]);
     jt[3] = rqei*2.0*height*(psf_r[l]*dz_r[l]+psf_c[l]*dz_c[l]);
-    jt[4] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = rqei/((double)fit_data->bg_counts[k]);
 
     /* Calculate jacobian. */
     t1 = 2.0*(1.0 - xi/fi);
diff --git a/storm_analysis/sa_library/dao_fit.c b/storm_analysis/sa_library/dao_fit.c
index 220ca93a..7eaa2f6b 100644
--- a/storm_analysis/sa_library/dao_fit.c
+++ b/storm_analysis/sa_library/dao_fit.c
@@ -86,7 +86,8 @@ void daoCalcJH2DFixed(fitData *fit_data, double *jacobian, double *hessian)
     jt[0] = rqei*e_t;
     jt[1] = rqei*2.0*a1*width*xt*e_t;
     jt[2] = rqei*2.0*a1*width*yt*e_t;
-    jt[3] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[3] = rqei/((double)fit_data->bg_counts[k]);
 
     /* Calculate b vector. */
     t1 = 2.0*(1.0 - xi/fi);
@@ -163,7 +164,8 @@ void daoCalcJH2DFixedALS(fitData *fit_data, double *jacobian, double *hessian)
     jt[0] = t1*e_t;
     jt[1] = t1*2.0*a1*width*xt*e_t;
     jt[2] = t1*2.0*a1*width*yt*e_t;
-    jt[3] = t1;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[3] = t1/((double)fit_data->bg_counts[k]);
 	  
     /* Calculate b vector. */
     t2 = (fi - fit_data->as_xi[k]);
@@ -238,7 +240,8 @@ void daoCalcJH2DFixedLS(fitData *fit_data, double *jacobian, double *hessian)
     jt[0] = rqei*e_t;
     jt[1] = rqei*2.0*a1*width*xt*e_t;
     jt[2] = rqei*2.0*a1*width*yt*e_t;
-    jt[3] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[3] = rqei/((double)fit_data->bg_counts[k]);
 
     /* Calculate b vector. */
     t1 = (fi - fit_data->x_data[k]);
@@ -310,7 +313,8 @@ void daoCalcJH2DFixedDWLS(fitData *fit_data, double *jacobian, double *hessian)
     jt[0] = rqei*e_t;
     jt[1] = rqei*2.0*a1*width*xt*e_t;
     jt[2] = rqei*2.0*a1*width*yt*e_t;
-    jt[3] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[3] = rqei/((double)fit_data->bg_counts[k]);
 
     /* Calculate b vector. */
     t1 = (fi - xi)/xi;
@@ -378,7 +382,8 @@ void daoCalcJH2DFixedFWLS(fitData *fit_data, double *jacobian, double *hessian)
     jt[0] = rqei*e_t;
     jt[1] = rqei*2.0*a1*width*xt*e_t;
     jt[2] = rqei*2.0*a1*width*yt*e_t;
-    jt[3] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[3] = rqei/((double)fit_data->bg_counts[k]);
 
     /* Calculate b vector. */
     t1 = (fi - xi)/fi;
@@ -448,7 +453,8 @@ void daoCalcJH2D(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = rqei*2.0*a1*width*xt*e_t;
     jt[2] = rqei*2.0*a1*width*yt*e_t;
     jt[3] = rqei*(-a1*xt*xt*e_t-a1*yt*yt*e_t);
-    jt[4] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = rqei/((double)fit_data->bg_counts[k]);
     
     /* Calculate b vector */
     t1 = 2.0*(1.0 - xi/fi);
@@ -527,7 +533,8 @@ void daoCalcJH2DALS(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = t1*2.0*a1*width*xt*e_t;
     jt[2] = t1*2.0*a1*width*yt*e_t;
     jt[3] = t1*(-a1*xt*xt*e_t-a1*yt*yt*e_t);
-    jt[4] = t1;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = t1/((double)fit_data->bg_counts[k]);
 	  
     /* Calculate b vector. */
     t2 = (fi - fit_data->as_xi[k]);
@@ -632,7 +639,8 @@ void daoCalcJH2DLS(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = rqei*2.0*a1*width*xt*e_t;
     jt[2] = rqei*2.0*a1*width*yt*e_t;
     jt[3] = rqei*(-a1*xt*xt*e_t-a1*yt*yt*e_t);
-    jt[4] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = rqei/((double)fit_data->bg_counts[k]);
 	  
     /* Calculate b vector. */
     t1 = (fi - fit_data->x_data[k]);
@@ -706,7 +714,8 @@ void daoCalcJH2DDWLS(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = rqei*2.0*a1*width*xt*e_t;
     jt[2] = rqei*2.0*a1*width*yt*e_t;
     jt[3] = rqei*(-a1*xt*xt*e_t-a1*yt*yt*e_t);
-    jt[4] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = rqei/((double)fit_data->bg_counts[k]);
 	  
     /* Calculate b vector. */
     t1 = (fi - xi)/xi;
@@ -780,7 +789,8 @@ void daoCalcJH2DFWLS(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = rqei*2.0*a1*width*xt*e_t;
     jt[2] = rqei*2.0*a1*width*yt*e_t;
     jt[3] = rqei*(-a1*xt*xt*e_t-a1*yt*yt*e_t);
-    jt[4] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = rqei/((double)fit_data->bg_counts[k]);
 	  
     /* Calculate b vector. */
     t1 = (fi - fit_data->x_data[k])/fi;
@@ -852,7 +862,8 @@ void daoCalcJH3D(fitData *fit_data, double *jacobian, double *hessian)
     jt[2] = rqei*(-a1*xt*xt*e_t);
     jt[3] = rqei*2.0*a1*a5*yt*e_t;
     jt[4] = rqei*(-a1*yt*yt*e_t);
-    jt[5] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[5] = rqei/((double)fit_data->bg_counts[k]);
 
     /* Calculate b vector. */
     t1 = 2.0*(1.0 - xi/fi);
@@ -946,7 +957,8 @@ void daoCalcJHZ(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = rqei*2.0*a1*a3*xt*e_t;
     jt[2] = rqei*2.0*a1*a5*yt*e_t;
     jt[3] = rqei*(-a1*xt*xt*gx*e_t-a1*yt*yt*gy*e_t);
-    jt[4] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = rqei/((double)fit_data->bg_counts[k]);
     
     /* Calculate b vector. */
     t1 = 2.0*(1.0 - xi/fi);
@@ -1090,7 +1102,16 @@ int daoCheck2D(fitData *fit_data){
   else if(peak->params[XWIDTH] > dao_fit->width_max){
     peak->params[XWIDTH] = dao_fit->width_max;
   }
-  
+
+  /*
+   * The 2D model has a single width, but the peak shape is drawn from
+   * XWIDTH in x and YWIDTH in y. Copy it after the clamp, otherwise a
+   * clamped peak is drawn with an unclamped YWIDTH. This is also the
+   * only place that multi-plane DAO fitting, mpDaoUpdate(), gets its
+   * YWIDTH from.
+   */
+  peak->params[YWIDTH] = peak->params[XWIDTH];
+
   return 0;
 }
 
@@ -1110,11 +1131,22 @@ int daoCheck3D(fitData *fit_data){
 
   peak = fit_data->working_peak;
   dao_fit = (daoFit *)fit_data->fit_model;
-  
-  if(daoCheck2D(fit_data)){
+
+  if(mFitCheck(fit_data)){
     return 1;
   }
 
+  /*
+   * Width range clamp, XWIDTH and YWIDTH independently. Not done by
+   * calling daoCheck2D() as that ties YWIDTH to XWIDTH.
+   */
+  if(peak->params[XWIDTH] < dao_fit->width_min){
+    peak->params[XWIDTH] = dao_fit->width_min;
+  }
+  else if(peak->params[XWIDTH] > dao_fit->width_max){
+    peak->params[XWIDTH] = dao_fit->width_max;
+  }
+
   if(peak->params[YWIDTH] < dao_fit->width_min){
     peak->params[YWIDTH] = dao_fit->width_min;
   }
diff --git a/storm_analysis/spliner/cubic_fit.c b/storm_analysis/spliner/cubic_fit.c
index 096a76e0..eee137de 100644
--- a/storm_analysis/spliner/cubic_fit.c
+++ b/storm_analysis/spliner/cubic_fit.c
@@ -89,7 +89,8 @@ void cfCalcJH2D(fitData *fit_data, double *jacobian, double *hessian)
     jt[0] = rqei*peak->psf[j];
     jt[1] = -rqei*height*dxfAt2D(spline_fit->spline_data,l+y_start,m+x_start);
     jt[2] = -rqei*height*dyfAt2D(spline_fit->spline_data,l+y_start,m+x_start);
-    jt[3] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[3] = rqei/((double)fit_data->bg_counts[k]);
     
     /* Calculate jacobian. */
     t1 = 2.0*(1.0 - xi/fi);
@@ -163,7 +164,8 @@ void cfCalcJH3D(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = -rqei*height*dxfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
     jt[2] = -rqei*height*dyfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
     jt[3] = rqei*height*dzfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
-    jt[4] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = rqei/((double)fit_data->bg_counts[k]);
     
     /* Calculate jacobian. */
     t1 = 2.0*(1.0 - xi/fi);
@@ -245,7 +247,8 @@ void cfCalcJH3DALS(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = -t1*height*dxfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
     jt[2] = -t1*height*dyfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
     jt[3] = t1*height*dzfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
-    jt[4] = t1;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = t1/((double)fit_data->bg_counts[k]);
 
     /* Calculate jacobian. */
     t2 = (fi - fit_data->as_xi[k]);
@@ -325,7 +328,8 @@ void cfCalcJH3DLS(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = -rqei*height*dxfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
     jt[2] = -rqei*height*dyfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
     jt[3] = rqei*height*dzfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
-    jt[4] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = rqei/((double)fit_data->bg_counts[k]);
 
     /* Calculate jacobian. */
     t1 = (fi - fit_data->x_data[k]);
@@ -406,7 +410,8 @@ void cfCalcJH3DFWLS(fitData *fit_data, double *jacobian, double *hessian)
     jt[1] = -rqei*height*dxfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
     jt[2] = -rqei*height*dyfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
     jt[3] = rqei*height*dzfAt3D(spline_fit->spline_data,zi,l+y_start,m+x_start);
-    jt[4] = rqei;
+    /* The background is shared with any overlapping peaks, see mFitCalcErr(). */
+    jt[4] = rqei/((double)fit_data->bg_counts[k]);
 
     /* Calculate jacobian. */
     t1 = (fi - xi)/fi;
diff --git a/storm_analysis/test/test_multifit.py b/storm_analysis/test/test_multifit.py
index 47b5f2af..8e8f6856 100644
--- a/storm_analysis/test/test_multifit.py
+++ b/storm_analysis/test/test_multifit.py
@@ -337,9 +337,10 @@ def test_mfit_8():
              "z" : numpy.array([16.0, 26.0])}
     mfit.newPeaks(peaks, "text")
 
-    # Round trip verification.
+    # Round trip verification. The 2D model has a single width, so ysigma
+    # comes back as the (clamped) xsigma, not as the ysigma asked for.
     for pname in peaks:
-        pvals = peaks[pname]
+        pvals = peaks["xsigma"] if (pname == "ysigma") else peaks[pname]
         mvals = mfit.getPeakProperty(pname)
         for i in range(pvals.size):
             assert(abs(pvals[i] - mvals[i]) < 1.0e-6)
@@ -402,9 +403,10 @@ def test_mfit_10():
              "z" : numpy.array([16.0, 26.0])}
     mfit.newPeaks(peaks, "hdf5")
 
-    # Round trip verification.
+    # Round trip verification. The 2D model has a single width, so ysigma
+    # comes back as the (clamped) xsigma, not as the ysigma asked for.
     for pname in peaks:
-        pvals = peaks[pname]
+        pvals = peaks["xsigma"] if (pname == "ysigma") else peaks[pname]
         mvals = mfit.getPeakProperty(pname)
         for i in range(pvals.size):
             assert(abs(pvals[i] - mvals[i]) < 1.0e-6)