We're going to keep you on your toes. :)
From the FAQs:
Your Average Score will be based on multiple best scores within ONLY your current Tier, not scores that you shot when in previous Tiers, which better reflects your current skill competing with the tee boxes and green speeds in your current Tier. Your Average Score will be based on ONLY your best scores, so completing a bad round will not negatively impact your Average Score or Tier. So be sure to finish all your rounds and gain the extra experience points, as a bad day won’t matter."
It needs to be updated to reflect the recent changes including match play.