I appreciate your feedback! Sorry to hear about your yellow, I didn't have my older fish for very long, but I was extremely attached to my bird wrasse and heni when they passed (estimated age was over 12) that's great though that they lived to their full lifespan.I would consider putting a background (black contact paper) on the back, and moving the rockwork against the back wall. Building up the hardscape around the overflow works really well, as there are the dark corners where the overflow meets the back wall at a right angle that make a good start on a great little hideaway (and are a two-points-of-contact spot to help stabilize the rocks). There's really not that much for good hiding spots in there, judging from the photo -- it is all round rocks, with little in the way of dark crevices.
Just my opinion on fighting with trying to keep a couple tangs in a 90 for quite some time (my 15 year old yellow died within the last year, and my same-age scopas is still with me). If it helps you, great; if not, maybe it will another reader. Seems to be an extraordinary many tang issues reported here, so I think all possible improvements are worth considering.
The back of the tank actually has black contact film already and that wasn't working so that's why I did the white paper (which helps a lot)
And the rockwork may look like it doesn't have a lot of hiding spots but it definitely does, I purposely built the rockwork around the back mostly and around the overflow to include many caves and good hiding spots because I knew i needed more spots than it was previously set up as. I'll see if I can get some good pictures