From WIS' BETA recruiting guide:
- Perimeter Offense (credit is adjusted based on the school's tendency for perimeter shots in the current season, which is determined using percent of total FGA that are 3-pointers)
Paint is just the compliment of Perimeter (i.e Perimeter score + Paint score = 100%) so if you're VG at Perimeter, you'll be likely VB at Paint and vice-versa or Neutral at both.
So to answer your question its determined by your present 3PT shots taken divided by Total shots taken.