orangehole: So somehow I advanced with an average above 63.0 and less then 40 ranked games in my tier. So there must be some consideration taken into the coin games.
Dunno about coin games (and no reason NOT to believe WGT in this respect), but I see that you've achieved quite a few vg results in RGs, winning credits. This makes any traditional tiering rules obsolete - averages, numbers!
I've yet to see any calculation for this effect, alas:
Congrats to your new tier!