Clarification, the rankings are based on your "available" points, which is the number shown by your name. For example, right now it shows you as having 238

. If you join a 200 point buy-in game, you'll be down to 38

available and you'll be ranked based on that.
In some way that seems silly, but then counting points that you've already spent in a game and might not get back also seems silly in some ways. So there you have it.