do your self heals always go off when you are below 100% health?
I find that most of the time my healers have already topped me up so any self heal I am doing are wasted, in which case the WH relic will come up tops as most of your self heals are just over heals.
If my self-heal overheals, then it's on the healers. Any overheal in the self-heal should be credited (demerited?) to them. This isn't necessarily a bad thing though. Unless your healers are having pathological energy problems, overheal is a non-issue. If I weren't overhealing on my self-heal, my healers would be overhealing even further on their main heals. It all balances out.
The important thing is that the self-heal contributes to the actual net survivability. Under circumstances where healing is actually tight and difficult to manage (Nightmare Jarg and Sorno, or HM Dread Guard), my self-heal overheal drops literally to zero. This is because my healers know how to take advantage of my survivability when they have to. For this reason, I feel pretty justified in counting the self-heal fully toward my survivability budget.