What can I be doing better?

I have Empress of India tropaeloum in the same DWC as Alaska Mix and Jewel Mix. For some reason, the Empress of India is much slower growing and getting a bit more burnt than the other two. I assume I fundamentally messed up putting different types in the same tank? They're surviving, but obviously the Alaska Mix is thriving while the Empress is slow growing and a bit burnt.

Any suggestions other than moving them to a separate tank? The obvious hindsight is 20/20 is that I'll never be putting different types in the same tank, because it's clear they prefer different conditions.