phiber:As I understand it, the system looks at you previous 15 lowest rounds to determine your avearage and that is how you progress. As you reach a certain level with say 25 ranked rounds and your average is say 63.4 and you shoot a 68, your average is not affected. Just before I turned Legend, I played St Andrews with high winds and shot a 67. My average when I did that was 61.1 and it didn't go up at all. That was why I sought the same information.
Quite rite Phi, only the number of lowest rounds in the calculation varies with the tier. It's equal to the minimum number of scored rounds neccessary to tier up.
For Legends, the number is 400.
Edit: A high score like that 68 would influence the average only if an even higher number was still in calculation. This usually comes into effect when a player just filled up the full no. of ranked rounds in his new tier. Then, a score above average may kick out a higher score and thus reduce the average.