We estimate the percentage of a player's shot attempts that come from each of three regions. Then when the player attempts a shot in the SimEngine we look at those percentages to determine the range of that particular shot, where Perimeter is strictly from behind the three-point line.
The range of a shot has no bearing on the odds of making the shot as that should work itself out over the course of a game. These percentages are helpful when gameplanning with the defensive positioning setting. If you're facing a team that is predominantly featuring high Paint%, then you'd want to focus your defense on the paint and vice versa for Perimeter.