stiff in the roll back

Doing a few rollbacks on Whizzy yesterday and he was stiff to the right ie I'd neck rein him to the right after stopping or backing and he would bend left and eventually roll back but leading with his shoulder to the right which is incorrect. I softened his jaw by pulling the left rein to my sternum and bumping with the right foot at the belly when backing to lift him up in the belly and give with his jaw. I also made sure when I pulled his head to the right with the direct rein that he gave his nose first then head and neck and his feet came along immidiately which I accomplished by bumping him in the shoulder- he can deal with being bumped in the shoulder if his neck is bent the other way and his head tipped- in other words he is pretty bent towards the direction he is going.