I have never been in the top eight of my ladder, and started at bronze. Now I'm at platinum. You are only promoted via your hidden rating, not your points or bonus pool or any of that hokus pokus. I play very little compared to most players, but digest each game thoroughly before moving to my next one. All you have to do to be promoted is beat players that are in the league above you more than 60% of the time, and be placed against the league above you constantly.