Caculate stacking lip support based on an angle

Removes the need for a magic constant.

standard.scad

@@ -80,7 +80,6 @@ h_lip = 3.548;
 d_wall2 = r_base-r_c1-d_clear*sqrt(2);
 d_magic = -2*d_clear-2*d_wall+d_div;
 
-
 // ****************************************
 // Stacking Lip Constants
 // Based on https://gridfinity.xyz/specification/
@@ -96,10 +95,19 @@ stacking_lip_height =
     stacking_lip_wall_height_mm +
     stacking_lip_outer_slope_height_mm;
 
-// Extracted from `profile_wall_sub_sub`.
+// Height of the innermost section.
+// Used to keep the innermost lip from just being a triangle.
+// Spec implicitly expects wall width to equal stacking lip depth,
+// so does not define this.
 stacking_lip_support_wall_height_mm = 1.2;
+
+// Support so the stacking lip is not floating in mid air
+// when wall width is less than stacking lip depth.
+stacking_lip_support_angle = 45;
+
 stacking_lip_support_height_mm =
-    stacking_lip_support_wall_height_mm + d_wall2;
+    stacking_lip_support_wall_height_mm
+    + tan(90 - stacking_lip_support_angle) * stacking_lip_depth;
 
 // ****************************************
 // Base constants