I practised alot before playing ranked rounds and when I did my average started low and stayed low.
Hack to Amateur - 5 Ranked Rounds
Amateur to Pro - 10 Ranked Rounds
Pro to Tour Pro - 20 Ranked Rounds
Don't know above that as I'm not there yet, also couldn't tell you the averages as I had a very low average...my average is still pretty low but I expect this to change when I get to Master lol
Cheers
DD