diff --git a/engine/MUNGA_L4/L4VIDEO.cpp b/engine/MUNGA_L4/L4VIDEO.cpp
index 58a3083..43ddfb9 100644
--- a/engine/MUNGA_L4/L4VIDEO.cpp
+++ b/engine/MUNGA_L4/L4VIDEO.cpp
@@ -3490,8 +3490,30 @@ DPLRenderer::DPLRenderer(
 		// while the cockpit-surround window is sized independently -- pinning to them
 		// would shrink the backbuffer and break the composite.)
 		//
+		//
+		// COCKPIT SURROUND: the backbuffer IS THE CANVAS, whatever the window
+		// happens to be (2026-07-26).  Everything downstream assumes it --
+		// BTApplyWorldViewport and BTDrawCockpitPanels lay out from the
+		// BACKBUFFER size, while the letterbox and the mouse hit-test map
+		// through gBTCockpitCanvasW/H.  Pinning to the client instead is fine
+		// only while client == canvas, which is true for a normal boot and
+		// FALSE for -fit: the window is the whole monitor before the device
+		// exists, so the backbuffer came out 3440x1440 against a 1452x1059
+		// canvas.  Field report: tiny MFDs hugging the corners, an over-wide
+		// world view, the scene squashed horizontally as Present scaled the
+		// oversized backbuffer into the letterbox -- and, unseen, every button
+		// hit-tested in a different space from the one it was drawn in (the
+		// exact #50 divergence the note above warns about).
+		//
+		extern int gBTGaugeCockpit;
+		extern int gBTCockpitCanvasW, gBTCockpitCanvasH;
 		RECT rc;
-		if (hWnd != NULL && GetClientRect(hWnd, &rc)
+		if (gBTGaugeCockpit && gBTCockpitCanvasW > 0 && gBTCockpitCanvasH > 0)
+		{
+			mPresentParams.BackBufferWidth  = (UINT)gBTCockpitCanvasW;
+			mPresentParams.BackBufferHeight = (UINT)gBTCockpitCanvasH;
+		}
+		else if (hWnd != NULL && GetClientRect(hWnd, &rc)
 			&& rc.right > rc.left && rc.bottom > rc.top)
 		{
 			mPresentParams.BackBufferWidth  = (UINT)(rc.right - rc.left);