Jump Ball Administration

[johnnyrao]

A1 is lining up during a jump ball facing the center circle about even with the 28 foot line. His back is to Team A's basket. Team A has a pre-set play since their center is about 5 inches taller than Team B's center. The play is designed so A's center tips direct to A1 who turns and drives towards the basket. I had seen this team do this in a prior game. As the teams line-up for the tap B1 lines up behind A1 so he can not turn and drive towards the basket. I am positioned next to Team A's coach ready to chop the clock to start the game. He keeps telling me that B1 can not line up behind his player. I did not call it becuase I think that as long as they are not on the center circle there is nothing wrong with this. I don't say anything either because I am not sure (I think I'm right). After looking it up in the rule book I can not find a specific reference to this being wrong. I still believe I am right on this and, as long as they are not on the circle, there is nothing wrong with this. B1 was not so close that A1 could not get a full step if he had the ball and turned around. Am I correct and, if not, can someone tell me where this is in the rules. I have this team again in a few weeks and it may come up again.