Every time I check for open invites, it's always the same two people. Plus, myself, but I can't see my invites for obvious reasons. I get the feeling on BK that players are very protective of their ratings and not really willing to defend them openly. Or, I think they only want to play people of a much lower skill level so they know there's no risk for them. It's a shame because I think there are a lot of good players and there should be more open competition.