As the others have said, the trigger should be covered 100% - in any of it's operating conditions (or put another way - trigger guard 100% covered by the holster). That said, one critical dimension (for me) is hand clearance to grab the grip when drawing. What's critical is where the belt is relative to the grip (ride height) - and material covering the trigger guard. With lower riding holsters, the grip is just above the belt line making it harder to get your hand around the grip fully to draw. In 1 instance, with a holster I really liked, I gave the maker this critical dimension which he accommodated (was kydex though). There are a lot of considerations that go into choosing a holster that works for you - especially if you tend to be a bit particular (as I am).