I recently had the same issue. I just called Horizon and ordered the servo I was using Reversed. Worked perfectly. I could have used a separate channel, but I'm using 2 receivers and wanted some simplicity. One servo in the elev port on one rx, the the reversed servo in the other elev port on the second rx. Yeah, I could have still mixed it but just wanted to do it this way.
Reversing Y harnesses have thier place, but I don't think they should be used on a control surface.