With 640×512 I’m able to adjust vertical size and position of the X68000 image, but not horizontal size & position. Would supporting these native resolutions enable that?
You should see the image become narrower when lowering H.samplerate. Adding the resolutions to the list won’t make a difference because they are mostly just presets.
This is in passthrough for 640×512 if IRCC. So setting this to 2x would make it look better?
That depends on the scaling quality of your display. 2x should be sharper on most displays.