If you look at all of us who have been moved to Tour Champion you will see that most of us have much higher averages than before. It appears that the saturation factor goes away and something else is used.
Every time a player tiers up, the player's average resets. At this point, we don't know if players will saturate at TC tier. Most likely they will. Nevertheless, everyone has (at most) a handful of rounds at their new tier.
We'll only find out if there is a saturation point when players stop seeing their averages fluctuate (i.e. going up or down). Also, if there is a saturation point, it's reasonable to assume it's at least 200 rounds.