The Wiz are last in the league in rebounding. So the logical place to point is McGee and Blatche. However, McGee and Blatche are averaging 9.8 and 8.0 rebounds per 36 minutes. Armstrong and Yi are averaging 7.9 and 4.3 rebounds per 36 minutes.
The other factor to consider is the number of rebounds to be had. The Wiz are also last in the league in opposing team FG%. Rebounding isn't the only issue.