I feel like I'm missing something. Is there a way to ensure Restoring (Healing) Breath targets me? It seems to target whoever has the lowest HP% in the party.
That's exactly how it works. It targets whoever is at the lowest HP%. You can increase the chances that this is you by swapping in huge HP+ gear on activation(there is enough time after activation and before the breath lands to swap to potency gear), but that's about it.