Well without seeing how your doing the snap, I'd say the zoom should modify the snap by a percent.
So if your snap was 25 with a zoom of 100 % it would be more like 50.
Exactly! I'm just not entirely sure how to put that into the expression. I've messed around with it but no luck. The cursor snaps to the mouse like so:
Cursor.x = int(MouseX/8)*8
Cursor.y = int(MouseY/8)*8
8x8 tiles, of course. Zoom goes by the hundreds, 100%, 200%, 300%, etc.