I agree with MelonHead. Get 10% of the difference between the two fighters if you, the lower point fighter, beats the higher point one.

I strongly disagree with only being able to challenge people within a certain point value. Both players might love to have a chance to fight each other but realize they may only do so if one of them looses tons of points if the other is unlikely to gain enough points. Well, I suppose you could just say "then don't do a ranked battle together" but that would still be at least mildly annoying.

No comment on if you loose points or not.