The team is in need of a rebounder in the starting 5 and its simply not Randolph. Randolph will never have a bigger position other than sixth man because he plays for himself trying to look good. Its better he comes off the bench because he can simply score, and could play a lot of positions to give players rest.
The two players that are really competing with each other is Mozgov and Turiaf. Mozgov need to show his aggressiveness in rebounding the ball, if he can show he is capable, the job is his. Turiaf has better awareness and can rebound, this is why he might win the center position.