A little bit of both. Of course this is really only relevant in M2M, given that a zone might have different coverage schemes, but I've been under the impression that an "open shot" is a result of good offensive flow, but if you've got a strong shooting PF and a weak OD opponent at PF (say 9 JS vs 2 OD) then it's going to be more the quality of the shot that improves (and hence the shooting percentage) than being more "open". Just my opinion of course.