As I've said before, Amauri works better in a system with wingers and a lot of wide play. He is a target man who holds up the ball for the recruits to come storming up the pitch. Since our only width is from the fullbacks, they usually don't get forward quick enough to provide an outlet for Amauri. And since the fullbacks are the players providing crosses, we don't get many of those chances, which Amauri is supposed to excel at.
In the 4-3-1-2, Amauri is indeed always playing with his back towards goal as his only support is from right behind him. He doesn't have any support out wide, which means his link up play isn't going to be utilized as much, along with the fact he's a lazy ass who doesn't make through runs.
Get Amauri some width and he'll do better, like he did when we deployed the 4-2-3-1 or straight 4-4-2. But even so, he's still not good enough and we should be looking elsewhere.