Is the XS-Pro's front-thread the same size as the F-Pro's, or is it smaller since the XS-Pro itself is thin? I'm just curious because if there's one thing I hate, it's a small profile front-thread which causes lens caps to have problems staying on (whether it be the old Canon models or the new "center-pinch" models). I've lost a couple of lens caps in the past because they couldn't stay on properly (using another brand of filters).
The XS-Pro thread has a lower profile, so there's a gap - but it's not big, I'd say about 0.75mm. The F-Pro has a gap, too, though its slightly smaller:
I've never had issues with caps popping off either filter, and I take lenses in and out of various bags a lot.