For your avg that 40 is x2, to reflect an 18 hole round = 80
So if your 2nd ranked round is a 35, x2=70.
80 + 70 = 150, divided by number of rounds played (2) = 75 avg, and so on...
Take a note of how many ranked rounds you have played at your new tier, then you will know when your avg 'saturates' and tiering up again becomes possible.
Congrats!