I think this is an area where coaches differ. On the Backspin every single coach that teaches Mishin's technique will have you keep the shoulders facing to the right on backspins, the idea being you want as little movement in the upper body with the exception of arms coming in. Even at full spinning speed the shoulders are checked to the right and the arms are in close to the body.
That then translates back to every single jump entrance (bar the waltz or axel) - shoulders are checked round to the right and the speed of the arms coming in is what controls rotational speed and that checked position to the right is the entrance to every single jump, again bar the waltz or axel, the air position you achieve, and the checked landing position on the exit.
Most coaches I've come across teach that the right arm coming in is what controls the rotation on the backspin, but the left arm pulling out is what controls the rotation on a forward spin so you end up with shoulders square. Some of the Mishin technique coaches, however, are teaching a shoulders checked to the right position on a forward upright spin. I had varying degrees of success trying it, but usually default to using the left arm on forward spins and ending up with shoulders square.