For mine, they don't seem to care where they're placed, high or low and I just have dual 96 w PCs. They do need at least a little flow. I have quite a few different ones and they all act differently. Some close/shrink then open daily. One I just got recently got covered in algae. It just looked like it turned green. The polyps didn't come out for almost 2 weeks. Then I moved it out in the light a little more where it could also get a little more flow and now it's orange and opened up, polyps out, just like when I bought it again.
Try different things. They're pretty tough and it looks like you have some pretty nice equipment running for it to be much of a water problem.
If you dose Iodine/Iodide, be sure you aren't using too much. If it gets too high, they're kind of sensitive and the polyps won't come out then either until it goes down again.
They all shed a layer of algae from time to time which looks like a layer of skin coming off them and they will shrink and sometimes turn pale white at that time.