I found this in the brochure for Telarc's 1812 ( Eric Kunzel and the Cincinnati Pops):
" ...On most systems all six amplifier output channels will be used for the five main channels plus subwoofer. The LFE output from the disc player itsef wiil then be connected to an independent single channel amplifer or directly to self-amplified speaker(s). A pair of small speakers may be placed high on the side walls midway between front and rear sorround speakers. Alternately, a single small speaker may be placed over and above the central listening position. .... Set the playback level to be equal to the main channels."
So there are some recordings out there with discrete height information if you want to give it a try.