It seems to me that weighted averages tend to discount "freakish" one-off exceptions from a player's usual scores. If you wanna move your average down or up, it looks to me that it takes several results in "that other range" (consistently, for a couple of rounds at least) to move your average score in a new direction.
The thread starter has been pretty stable in posting rounds of about 32 or so recently, but there is an odd round of 40, and now 30, among those more usual scores of his. It looks like his weighted average discounts these rounds as "exceptions" and (for now) holds on to that 64.xx average that more accurately reflects his usual play.