Could you use a scaling factor in your collisions depending on the screen res?
TBH, that could get really messy and I'm not sure I could get it to work meaningfully, anyway.EdzUp: Yeah, that's the problem. It's unavoidable.
I basically need to decide:
a) Use world coords representation which is consistent regardless of screen mode, but the screen representation may not be 100% accurate.
b) Use the screen representation which is visually accurate, but may not be consistent between different screen modes.