Yup, I agree that height does not really matter to the game effect.
During the game, it should be down to the comparison of individual player at that position, such as SF vs SF, SG vs SG (of course this depends on the defensive assignment)...
As you can see my players
http://www.buzzerbeater.com/team/197874/players.aspx, one of the youngsters is mediocre at rebounding, however, he obtained 15 and 17 rebounds in two different games. I believe that position of the opponent might be pitiful / awful at rebounding, so he could get such high number of rebounds.