From the knowledge base:
- Every missed field goal attempt in a normal possession is rebounded. Rebounding looks at the real-life offensive and defensive rebounding percentages of all ten players on the court, though the shooter and his defender generally have less of a chance, especially in the case of a three-point attempt. We look at each one-on-one matchup for this situation (shooting team is still considered offense) to determine if one player has a better than average advantage over his opponent. These players will get a boost to their percentages, while their opponents will see their percentages drop. We then look at all ten modified percentages. The chance that an individual player has of getting the rebound is relative to how his percentage compares. If the ball is rebounded by an offensive player, there is a chance for a put-back. Assuming no put-back, the possession restarts. If the ball is rebounded by a defensive player that team begins its possession on offense.
Generally speaking, you want to try and have a reb edge at every position to get that "better than average advantage" over your opponent described above (what that number actually is, nobody will ever know).
As to your specific question above about a center and small forward; since most small forwards don't have those %'s it would be more advantageous to draft a SF that does have those numbers because you will likely gain that "better than average advantage" and be more likely to grab the rebound. However, if you draft a low reb% C, you'll likely be giving your opponent that advantage.
In sum: Practice. Read the forums. Study other teams. Roll the dice. Because in the end, this whole thing is just a crap shoot anyway. But it's still fun.