This sounds like the best option for me, but even if it was reliably working (or spawned pillars), the problem for me would be micro-managed positioning. So I know the UI was just implemented, but "more reliable" probably includes removing the 10%-100% mechanic altogether.
My random idea would be damage bonus while on full hp, damage reduction while not (or something close to this, I recognize the "getting oneshot" issue here). You could invest in shield gating/healing to keep the damage buff active, but if you want to build for tanking, it could be done.
(and I gotta shoot my shot, I would love if Hall of Mirrors was the helminth ability, even though just thinking about it would be enough to break the game's code)