Faceless Void staff Rigging problems

cagdasx44

I tried to make top rocks swing. So I rigged them to staff bone with most weight and also to skirts bone with less weight. But no matter how little I weight them to skirt they stlii change their position as skirt bone. How can I make the swing by using skirt bone but prevent position change.Here is a little sized gif to make you understand what I am talking about. THX!