I'm no kiltmaker, nor do I play one on the telly, but I think you have to make the adjustment from both sides. If you only move the buckles on the right hip, you'll end up with an outer apron that's much tighter than the inner apron and makes the inner apron bunch up. Besides, it's the inner apron that really does the work anyway. The outer one just covers it up. But they have to be balanced with each other so they lay properly with each other.

That's my take on it, anyway.