But thinking more logical here, you get more information out of it by having it show health deficit instead of health percentage.
This is due to the fact that you're technically already getting the percentage information by just looking at the health bar. If it's down to half, you know it's 50%, and so forth.
Good luck with your raid frames. It's an eternal problem of WoW as a healer, because you want as much information on them as possible; but you want to avoid cluttering them.