By hooking your thumb over the post and using your index finger to pull, you are essentially locking the release so that it does not fire during the draw. Until you get really.........really comfortable with the release, I suggest keeping all of the pressure on those two fingers. The same thing goes for letting down, hook your thumb over the post and relax your middle, ring and pinky as you let down.

You can put some pressure on the middle finger as it is right next to the pivot point and will probably not cause that much rotation of the release, however anything further out is just begging to have the release fire on you.