Your 24" fixture has a reflector? It can go on top of screen but the screen MUST be a wide hole type-- please get rid of the coil bulb--- I would get a 22" Reptisun 10.0 T 5 bulb for the 24" fixture it must have a reflector - a solid bright white basking bulb--- let me know what you decide to do the T 5 has different distances for the placement--