yikes, chalices definitely do not have a lot of meat on their bones to spare and they can really recede quickly. If your water conditions are indeed in the zone (and it looks like with all the coral in your tank that it probably is), flow and lighting are critical as you said. But you already have it placed in low light, so the next issue is somehow a lot of flow hitting it.
Sometimes even when you do everything right, a particular coral either came in to your tank unhappy or it is just peculiar and could not get comfy in your tank. Strange, indeed.