I agree with milwood above. My D3 zone team has a PF with good rebounding numbers (61ATH, 77REB, A IQ) that averages 9 RPG. My SF isn't great at rebounding (66 ATH, 32 REB, A IQ) and averages 4.1 RPG. The "ideal" C I posted earlier in the thread (65 ATH, 98 REB, A+ IQ) averages 9.6 RPG.
I play a lot of 2-3, even though I consider my SF more of a G type than a post type. Just looking back through past games, I also play a lot of minus in a 2-3, more than a few -5's.
Maybe it's the rebound logic that's been discussed before - decide which team gets the REB, then weighted formula to choose which player gets the actual REB. I don't think, in very limited eyeball tests, that REB is averaged between the SF and PF.