Raid boss health condition.

I have a new frost DK rotation I have been working on. It works EXCELLENT for everything but raid bosses (it even works great on adds during a raid boss fight. The issue I am running into is with Soul Reaper. It is set to only activate if the mobs HP is less than 35%. Problem is, on raid bosses it triggers that spell constantly, from 100% all the way down to 0%. I've done some checking around, and it doesn't have issues on dungeon bosses. I've only tested this in LFR style raids, not normal or flex yet.