Someone here told me that the quickest way to lower the average is to play and win match game against opponent with better average. I just won 5up in scored match play against Legend with 61 average and mine did not change at all, so I wonder why?
They have to be of a higher tier than you. However once you become legend this route is no longer available to you.
I'm thoroughly convinced that it's the fastest way to advance to TM and L tiers.