Index: trunk/psModules/src/imcombine/pmSubtractionMatch.c
===================================================================
--- trunk/psModules/src/imcombine/pmSubtractionMatch.c	(revision 18347)
+++ trunk/psModules/src/imcombine/pmSubtractionMatch.c	(revision 18348)
@@ -539,20 +539,18 @@
 
             // Set the variance factors
-            float xMid = 0.5 * (region ? (region->x0 + region->x1) : numCols); // Average x position
-            float yMid = 0.5 * (region ? (region->y0 + region->y1) : numRows); // Average y position
             switch (mode) {
               case PM_SUBTRACTION_MODE_1: {
-                  recordVarianceFactor(conv1, pmSubtractionVarianceFactor(kernels, xMid, yMid, false),
+                  recordVarianceFactor(conv1, pmSubtractionVarianceFactor(kernels, 0.5, 0.5, false),
                                        region);
                   break;
               }
               case PM_SUBTRACTION_MODE_2:
-                recordVarianceFactor(conv1, pmSubtractionVarianceFactor(kernels, xMid, yMid, false),
+                recordVarianceFactor(conv1, pmSubtractionVarianceFactor(kernels, 0.5, 0.5, false),
                                      region);
                 break;
               case PM_SUBTRACTION_MODE_DUAL:
-                recordVarianceFactor(conv1, pmSubtractionVarianceFactor(kernels, xMid, yMid, false),
+                recordVarianceFactor(conv1, pmSubtractionVarianceFactor(kernels, 0.5, 0.5, false),
                                      region);
-                recordVarianceFactor(conv2, pmSubtractionVarianceFactor(kernels, xMid, yMid, true),
+                recordVarianceFactor(conv2, pmSubtractionVarianceFactor(kernels, 0.5, 0.5, true),
                                      region);
                 break;