GotM is a simple multiplier on every damage event, based on your current health / max health. No complex arithmetic needed. (us.battle.net/wow/en/forum/topic/20743714421?page=11#218)
That said I'm not sure how practically useful it is since it doesn't change your decision process. It's nice as visual candy but doesn't have much value likewise for dodge chance.
Apart from cases where the tank is Celestalon that's tanking at 35% hp with perfect communication with the healer just to get the extra orbs and 'game' the system.