% Chance to increase potential tier?

I have wondered and thought about this alot too and I would place bets on 10% to epic and 5% to unique from all the stories I've read on the internet and my own cubing experiences. No idea about legendary and master cubes but I'm guessing they'll let it stay 5%. Going to 2.5% would be overkill. (Then again, Nexon and mathematics never really combined).