Hi TeeWade, once you tier up the counter resets and you will need to have a determined amount of ranked rounds for it to plateau and start counting down only. Now, that number I am not sure of, but until you get there every round is calculated into the big pot and your average will fluctuate until such a time. It is not a bad or good thing, it is what it is and makes no difference in the way you play and score, just keep playing and enjoy your rounds :))
Well done making it to TM btw.