diff --git a/src/experimental/sf_sphere.scad b/src/experimental/sf_sphere.scad
index 092ad95e..0beb5353 100644
--- a/src/experimental/sf_sphere.scad
+++ b/src/experimental/sf_sphere.scad
@@ -11,7 +11,7 @@ use <experimental/tf_sphere.scad>;
     invert: inverts how the gray levels are translated into height values.
 */
 module sf_sphere(levels, radius, thickness, depth, angle = [180, 360], invert = false) {
-    dp = is_undef(depth) ? thickness - .1 : depth;
+    dp = is_undef(depth) ? thickness / 2 : depth;
     surface = _sf_square_surfaces(levels, thickness, dp, invert);
     rows = len(levels);
     columns = len(levels[0]);
diff --git a/src/experimental/sf_square.scad b/src/experimental/sf_square.scad
index 59ea4d70..29312e71 100644
--- a/src/experimental/sf_square.scad
+++ b/src/experimental/sf_square.scad
@@ -8,7 +8,7 @@ use <experimental/sf_solidify.scad>;
     invert: inverts how the gray levels are translated into height values.
 */
 module sf_square(levels, thickness, depth, invert = false) {
-    dp = is_undef(depth) ? thickness - .1 : depth;
+    dp = is_undef(depth) ? thickness / 2 : depth;
     surface = _sf_square_surfaces(levels, thickness, dp, invert);
     offset_z = invert ? thickness : 0;