If you are set on using this type of fish instead of common feeder type fish.....you could use a blue moonlight after dark that would enable the fish to not go into their full "sleep" state in addition to the cover you mentioned.
I had my 190g tank set up with several types of predatory catfish and stingrays and wanted to include a type of cichlid as well.
I had a blue moonlight that was a spot light aimed at the middle 1/3 of the tank and the cichlids always spent the hours of darkness in that moonlight. It was very interesting to watch even during those hours of darkness because not only did the cichlids behave as I mentioned but the predatory catfish hung around just outside the blue light waiting to see if any of the cichlids would wander into the dark areas of the tank.
The stingrays showed no interest in the cichlids day or night.
