Heals are bigger on DPS than tanks.

So I play a Holy Paladin and I’m just now noticing that my heals are hitting bigger on dps than they are my tanks. I use Healbot for my healing add on and i have it configured for max rank Flash of Light, but I’m sitting in Mag’s right now and it’s hitting my tanks for ~1700 and the dps for ~2000-2100. Does anyone know why?