Stu's method but with masking tape on the un-cut side?
When you've marked and cut the real hole for the ball in the door, remove the remains of the tape.
Related question: How do you size your balls?
Seriously - if the door and frame are too close, the catch gets very hard to open, as the angle of contact between the ball catch and the striker plate is too severe. So you either have a larger gap (not pleasing), set either ball or plate in a bit more (possibly OK), or use a smaller-sized catch altogether and risk it going loose as the wood moves around.
It seems to me the ones with a "hollow" striker plate rather than just a hole are best, as they should keep the ball in the "just so" position irrespective of how the wood moves, but I've had trouble finding them these days (I take them off old furniture when I can).
Any thoughts?