I think the circles are just a graphic and don't really affect how much damage is done to you. Like in Garuda when it didn't matter if you were behind the pillars or not for her ultimate attack. We stacked inside of a circle and were just fine with heals and regens. The important thing is just that the group stacks so that the healers can top everyone off. The other part of the mechanic is that the 3 adds need to die before Final Verse or it's an instant wipe (our first attempt saw a lot of DPS deaths haha).