Duncanopsammia are actually quite picky LPS coral. They will open one they are 100% comfortable. I have a colony in a 5 year old established reef that will still take a few months to open, if I frag off a piece and move it to a different area of the reef. Best bet is to pick a spot, with medium light and leave it alone for a few months. If it is losing tissue, you may have another issue. If it is simply not opening, give it a lot of time. Every time you move it, you reset the clock.