This is how I would do. I would set for level brackets (70-79,80-89, etc etc) and +/- 5k power, with you power always rounded up(19001 would be considered 20k because it's higher than 19k).

Example is a Level 70 20k power player can fight a level 79 with 25k power but not a level 71 with 26k power.

I think that would make the fights more interesting.