Simple answer - you assign numbers to player based upon the ratio of distro that you want them to get in comparison to other players. Supposedly, the game will take the 5 players on the court and total their distro and create a percentage that a play is run for/thru them. So, it doesn't matter if you assign all 100 points as the game is only creating a ratio from the 5 on the court.
So, say you have 20, 10, 5, 5, 0 on the court. That will translate to 50%, 25%, 12.5%, 12.5% & 0. Of course, the player with 0 might get a put-back or something, but the plays won't be run to them. If you ended up with 20, 2, 1, 1, 1, then that would be 80%, 8%, & 3 @ 4%.
You can, and I suggest that you do, give everyone a 0 distro for the first exhibition game and see what the sim chooses to do. The sim will assign distro based on its own process (maybe good, maybe not). However, do go though and assign +/-. I suggest a rule of thumb of 90+ PER +2; 70+ PER; +1; 60+ PER 0; 50+ PER -1 and everything below 50 -2. Save to all defenses. After that first exhibition, set your distributions with the best guess from what you learned and save to all defenses again. Adjust from there.