I'm confused, if Amir is the 3rd big, who is the 2nd?

And I'm not exactly comfortable with him shooting 3's at this point, so I guess he is going to have to prove to me that he can do it, and the only way to do that is to shoot them. But he has to make them at a decent clip, or for me it's just a waste of a possession because it would be just as well to draw up a play for a 3 pointer from Lowry or one of the wings, and have
Amir battling for a rebound.