diff --git a/examples/sideboard/sideboard.py b/examples/sideboard/sideboard.py
index de6ccda..6e9420e 100644
--- a/examples/sideboard/sideboard.py
+++ b/examples/sideboard/sideboard.py
@@ -166,10 +166,14 @@ def find_body(name, comp=None):
     print(">>> Top: 1")
 
     # ==== KICK ====
-    # Anchor to Side_Left (clean Case body). KickFront_Sk is on the xZ plane
-    # (normal y); project Side_Left's front face (y,-1) at corner (0,0,kick_h)
-    # and let reanchor retarget the x/z origin dims (signs via abs()).
-    sk, pr = sp.sketch_rect_model(kick_c, kick_c.xZConstructionPlane,
+    # Anchor to Side_Left (clean Case body). KickFront_Sk is on an xZ-parallel
+    # plane RECESSED to y=kick_inset (the kick is set back from the case front
+    # for toe clearance). Sketching on the bare xZ plane (y=0) would flatten the
+    # y=kick_inset origin onto y=0 and build the kick flush with the front —
+    # the off-plane-origin bug. reanchor then retargets the in-plane x/z dims.
+    kick_f_pl = sp.off_plane(kick_c, kick_c.xZConstructionPlane,
+                             "kick_inset", "KickF_Pl")
+    sk, pr = sp.sketch_rect_model(kick_c, kick_f_pl,
         ("kick_inset", "kick_inset", "0 in"),
         {"x": "case_w - 2 * kick_inset", "z": "kick_h"}, "KickFront_Sk", ev)
     pr = (sp.reanchor(sk, ref_side_left, case_occ, "y", -1,
@@ -184,9 +188,12 @@ def find_body(name, comp=None):
     k_ymid = sp.off_plane(kick_c, kick_c.xZConstructionPlane, "case_d / 2", "KYMid")
     sp.mirror_feats(kick_c, [kf_ext], k_ymid, "KickBackMir").bodies.item(0).name = "Kick_Back"
 
-    # KickLeft_Sk on the yZ plane (normal x); project Side_Left's left face
-    # (x,-1) at corner (0,0,kick_h) and reanchor the y/z origin dims.
-    sk, pr = sp.sketch_rect_model(kick_c, kick_c.yZConstructionPlane,
+    # KickLeft_Sk on a yZ-parallel plane RECESSED to x=kick_inset (kick set in
+    # from the case side). Bare yZ (x=0) would flatten the x=kick_inset origin
+    # onto x=0 and build the kick flush with the side — the off-plane-origin bug.
+    kick_l_pl = sp.off_plane(kick_c, kick_c.yZConstructionPlane,
+                             "kick_inset", "KickL_Pl")
+    sk, pr = sp.sketch_rect_model(kick_c, kick_l_pl,
         ("kick_inset", "kick_inset + board_thick", "0 in"),
         {"y": "case_d - 2 * kick_inset - 2 * board_thick", "z": "kick_h"},
         "KickLeft_Sk", ev)
diff --git a/helpers/sp/sketch.py b/helpers/sp/sketch.py
index ef2d440..eb4d90b 100644
--- a/helpers/sp/sketch.py
+++ b/helpers/sp/sketch.py
@@ -158,6 +158,19 @@ def sketch_rect_model(comp, plane, model_origin, model_size,
         corner[a] += ev(expr)
 
     sk_o = sk.modelToSketchSpace(Point3D.create(ox, oy, oz))
+    # Guard: model_origin must LIE ON the sketch plane. modelToSketchSpace
+    # flattens the point onto the plane, dropping the out-of-plane component
+    # (sk_o.z) below — so an off-plane origin would silently create the body
+    # IN the plane, not at model_origin (the back-panel-at-front bug class:
+    # PR #56). Catch it here as an immediate, self-explaining error instead of
+    # a late interference. A correct call (plane at the right offset) has
+    # sk_o.z ≈ 0; only a wrong plane trips this.
+    if abs(sk_o.z) > 1e-4:
+        raise ValueError(
+            f"sketch_rect_model('{name}'): model_origin lies {sk_o.z:.4f} cm off "
+            f"the sketch plane — the body would be created IN the plane, not at "
+            f"model_origin. Sketch on an off_plane at that offset, or set the "
+            f"out-of-plane component of model_origin to match the plane.")
     sk_f = sk.modelToSketchSpace(
         Point3D.create(corner["x"], corner["y"], corner["z"]))