Your example just backs up what I said. 6-7 rpg is hardly comparable to the 15 rpg averages that half-decent PFs have in BB. You might be happy that your SF gets more rebounds than the competing SF but he still isn't pulling his weight when compared to the PFs and Cs. Which was what my observation was.
My own SF Roger Garcia
(4558156) has got 3 rebounds in the 2 games he's played at SF and 9 and 19 in the two games he's played at PF. Thats a much larger chunk of the rebounding pie he has access to by simply moving up a position.