You're wrong. Rebounding is done on a team basis, with rebounds later allocated to individual players. However, there are positional modifiers weighting the importance of each position to the team rebounding. In other words, when a rebound is determined, it compares each team's aggregate rebounding score. But that aggregate score isn't just the sum of the rebounding ratings of the players on the floor. It isn't even just the sum of the players' overall rebounding abilities (primarily some combination of REB and ATH, weighted heavily towards REB). It's something like 1*CTREB + 1*PFTREB + .5*SFTREB + .2PGTREB + .2SGTREB, where TREB is some total rebounding metric. Those numbers aren't precise, and I have decent numbers, but I won't give them away in extreme detail. As simple estimates those aren't horrible.