Height only matters for training. For example, if player A has the same exact same age, skills etc. as player B, but player A is 6'8 and player B is 6 '5 they will have the exact same chance at getting the rebound. Player A will train inside skills faster than player B and player B will train outside skills faster than player A.
Hope this helps, also if you don't mind posting your players skills I could help you more.