There's no fixed rate of improvement because of the nature of a WGT average. It includes just a certain number of your best scores in your tier, and now that you have advanced so well it depends on the scores in that calculation.
Assumed that 66 (33 for 9 holes) be the highest number in it, only 65 or better would better the average, replacing that 66. In that event, your average would decrease by .025. That said, you will certainly see each improvement in your average.
It's safe to say that you have higher scores than 60 (30 from you RG) in the mix for 63.15, therefore the average must have improved from that result.
Maybe it didn't from the 35 you played later?