Are they proportional to score or place? What the actual values added/subtracted to your belt based on these? I ask because it seems to me like it's a bit easier to go up than to go down.
That's what I don't like about it. I think it should have more to do with score, and less to do with place. I've been in high scoring games against higher-ranked players where I've finished in last, but still had a pretty respectable POSITIVE score of 3, and still lost like 9 BP. Often times I actually play pretty well, but get penalized just because obviously someone has to finish dead-last.
If they decide to do it like that, it should be relative score rather than just your score. To clarify, it should be your score compared with your enemy's score, but it should also be about what your belt is vs what their belt is because if you managed to get 15+ score against nubs, you'd get further than you actually deserved for the match.