Simple answers, sometimes difficult execution. Proper thumbhole size is when you can insert your thumb STRAIGHT and withdraw it straight. You want a bit of drag all the way around, because when you squeeze (you still have to squeeze slightly to hold onto the ball, you won't ever be able to completely relax your hand) you compress your thumb slightly. You don't want extra room, that will cause you to grip, and if it's too tight it just won't come out . . However, drilling a hole a bit size or two larger than what you need allows you to add tape which will both eliminate any kind of vacuum created by a thumbhole that fits TOO well, and give you something to hang onto, which reduces required grip pressure. Pitches, or angles are more a comfort thing, you want to angle so that it's comfortable and fits the way your hand naturally wants to sit so that you can hang onto the ball with the minimum amount of pressure possible. This is a bit of trial and error sometimes.
If you have a proper fit, you won't want much bevel. Bevel allows your thumb to move out of position above the thumbhole and can contribute to gripping/sticking. Most people need bevel because of how they grip the ball. When you bend your thumb and/or have a long span, the edge of the thumbhole is going to hit you hard. If you keep your thumb straight and have a proper span, you almost enjoy not having bevel, it's actually an aid. You don't want to cut yourself of course, so you might hit it slightly coming off the press, but not much.
Adjusting to a tighter thumbhole and less pitch or angle can be rough if you're used to gripping . . BUT, if you pair that with fixing your entire fit at the same time, it will actually feel more natural and it might be a lot easier than you think it will be.
How does one determine proper thumb hole size and pitches?
How does beveling play into this discussion?
How do you adjust to a tighter thumb hole and maybe less reverse pitch?
Thank You...
