[Matt]

I think it has to do with the fact that you must set up your selected hinge action in the backstroke. If you're horizontal hinging, you must swivel your left wrist to the plane going back so that you can have a full roll hinge action. With angled hinging, it's "no roll" going back and "no roll" going through. The backstroke left wrist action must match the downstroke action.

If you "no roll" going back and horizontal hinge (full roll) coming through, you're going to have a hooking problem on your hands. Same idea goes with swiveling going back and "no rolling" coming through - clubface stays open.

So you're not actually Hinging in the backstroke, you're just "getting everything ready."