I've noticed that the temperature in the pump compartment with the heater in there is higher than the rest of the tank. However, not to that extreme in my case (so far!).
On a side note, I couldn't find the Endler's Livebearer and figured it had died and there was simply no body to be found. I just so happened to mess with the air hose in the pump compartment and noticed the Endler's swimming in the compartment. It had jumped there from the main part of the tank! Needless to say it was a real pain to get it out of there. Ended up siphoning his ass out of there with some wide hose I had. Very stressful for both myself and the fish! Now I use the cover over the tank!
That's a tough spot!! I've stopped trying to shoo the juvenile RCS out of the back filter area and just do water changes really quickly
They just pop back up once there is water again like nothing ever happened. I'm awful.