tripelo,
Interesting exercise.
I experienced a similar phenomenon when I moved my single HDB8-X from my aluminum HAM tower leg (@ ~19’ AGL) to my TV tower mast (@ ~40’ AGL). Most stations got stronger (marginally), some stayed about the same, I lost one and picked up a couple of others. When I added a second HDB8-X to my TV tower array most channels signal strength improved 1-2 dB but at least one actually appeared to get weaker? The two HDB8-X’s are vertically stacked.
[IMG]http://forum.tvfool.com/attachment.php?attachmentid=799&d=1410727208[/IMG]
The HDB8-X I ordered to form my 16 bay array arrived pretty damaged (kinked reflector rods & 3 of the 4 bow-ties on one panel loose). Solid Signal replaced it for me and I installed the replacement on the TV tower. I straightened the bunged up antenna as best I could and hung it from the aluminum tower leg. Once again I started to receive the channel lost by moving to the TV tower. (If only I spoke Spanish it would do me some good)