Horford isn't really a volume post player, but there was at least one time where he was in the post with Rondo on him and he took turnaround jumpers instead of backing him down.
I think it's pretty minor, but he needs enough of a post game that teams can't exploit him.
I also think we got him the ball and then everyone was standing around watching him. Al Horford has had a AST/TO ratio over 2 the last 2 years on the Hawks which is pretty amazing for a big guy, and he's had a lot of assists through two games. When he has the ball, the C's should be looking to set backscreens for open looks, or making cuts into the lane.