From test in real live, wall could have more holes.

assets/wall.scad

@@ -46,7 +46,7 @@ module wall_mount_screws() {
 }
 
 module wall_holes_on_x() {
-    width_without_screws_margin = wall_width - wall_mounting_screws * 3;
+    width_without_screws_margin = wall_width - wall_mounting_screws * 2;
     width_without_margin = width_without_screws_margin - hole_entrance * 2;
     width = width_without_margin - width_without_margin % wall_holes_space;
 
@@ -59,7 +59,7 @@ module wall_holes_on_x() {
 
 module wall_holes() {
     hole_height = hole_entrance * 2 + hole_holding * 3;
-    height_without_screws_margin = wall_height - wall_mounting_screws * 3;
+    height_without_screws_margin = wall_height - wall_mounting_screws * 2;
     height_without_margin = height_without_screws_margin - hole_height;
     height = height_without_margin - height_without_margin % wall_holes_space;