I've been looking at some video of Belt and have spotted what I think is causing the problems with his swing. It's a much bigger issue than his stance or place in the box. It's so fundamental and easily fixed I can't believe they haven't addressed it.
Next time Brandon comes to the plate or if you have him on DVR check out the position of his top hand on the bat. Belt grips the bat in the palm of his hand back toward his thumb, not his fingers and it's way too strong a grip. His knocking knuckles are rotated so far forward they align with the back of his right hand.
This position makes it all but impossible to hit down on the baseball, rotate his wrists or pull a pitch on the inner half with much authority. No question it also hinders bat speed. It basically locks him up. The only location he can really get the barrel of the bat on the ball is middle-away and only with an uppercut swing.
How this kid has gotten as far as he has with that grip is amazing.
In this video Don Mattingly explains it perfectly and demonstrates exactly what Brandon Belt is doing incorrectly.
Lol Don even came up with a bat that helps get proper hand position. I've never seen this before. Good idea.