I'm in the same situation you are. I've had my 4" rhom now for around 4 weeks. Mine hasn't adjusted as well to his new home though. I had a few barbs and mollies in his tank before I brought him home. I didn't feed him for the first 2 weeks, he steadily picked off the tank mates. I now feed him pieces of shrimp every 2nd day. He hides in the corner all day and only ventures out when the lights go out. Even then he spends a lot of time trying to swim through the glass.. I notice mine is no where near as tall bodied as yours.
Try dimming your light until it adjusts to your tank - you could move the light to one end as well. Give the little guy the chance to choose the amount of lighting and it usually makes a difference. Fish love structure, and the main structure in your tank is also the brightest so this kind of cancels the fish's desire to go there. Although I do like your display, your P may like it more if you change it up.