I doubt any higher would make that much of a difference. I didn't realize they were already 12" off the top. Only thing I can think of (that is recommended a lot in the FW
forum, I'm assuming it's safe for SW
too) is just getting some cheap clip on fans and pointing them straight on the water surface. It will cause water to evaporate which will cool it.
Just keep an eye on your water because since it's evaporating faster you will have to top off more often.
edit: well i just went back and re-read and basically everyone recommended that. haha. except to do it on your sump/refuge instead of the main tank. has doing that helped you at all? or did you not do it yet?