So I’ve done a little digging around the code. No fix for the stretching yet, but if anyone wants to dive in it looks like the functions responsible for orientation/scaling are in: engine/src/framework/application.js
the auto generated start.js calls resizeCanvas() which, in case of ‘fill window’, calls setCanvasResolution(), which, interestingly, calls resizeCanvas() again.
innerHeight/Width and and what looks like a wrapper for css canvas.style.width/height determine what happens with the scaling.
just noticed this thread is a year old, but the problem is still here…