Quote Originally Posted by Archangel View Post
Except he's surrounded by the fox's chakra in this new form as well

And unlike the last time he's in complete control of himself and isn't suffering from the cloak's side-effects.
The true kishimoto answer is that the kyuubi was controlling the chakra to shape it for him. Like how Sasuke couldn't predict the chakra's movements with the sharingan, it had a mind of its own.