Perhaps my description doesn't give you a good visual image, but the bottom of this panel is at least 36" from the top of the firebox. There is a wooden mantle between. Anyway, if I have flames coming out of my gas fireplace that reach 5 feet, I've got bigger problems.

The "studs" over my fireplace were horizontal. I cut out the drywall and installed a piece of plywood to the 2x4s that were there. Taped, sanded and textured the plywood then painted it to match the wall. While I was going through all the trouble, I had an electrician install an electrical outlet.