As far as I know......WGT has yet to publish any criteria to go from the Champion Tier to the Tour Champion Tier.
I do believe that to become a "TOUR CHAMPION", it's by Invitation from WGT only.
I looked up the on the WGT list of players......there is ONLY (1) Tour Champion shown. She is a Level 104 player. Her avg. has moved slightly up above 57.00. She joined WGT in January of 2008......8 yrs. ago!!! You can go study her profile, it might give you some idea of what you might need to do to make "Tour Champion".
From looking at her "Scoring History"....it doesn't appear she's playing in Country Club games.....but, instead is playing WGT Tournaments (on Championship Speed Greens).
She has also posted approx. 2,000 games in the TOP 10 and 2000 games in the TOP 100.
Just an FYI.....currently, there are approx. 1,600 "Champion Tier" players here on WGT.
I know of a WGT Champion, who is Level 139, who I feel should be invited by WGT to be a "Tour Champion". He is YOBAN. He has hit over 24,400 ranked rounds....and has incredible stats!!!
Just today, as a Champion Tier player....I reached an Average of 56.99.....but, I'm not going anywhere.....LOL.