Oh man, that sucks. Sorry that my question caused such grief. But I do thank you for the info.

Right now my center is angled up 4° with MoPads. That's just about right. 17° would be too much, but if I use the MoPads backward with the spacer I can subtract 8 from that, and end up with 9° of up-tilt. That should be pretty close to what I need too.

Pioneer PDP-5020FD, Marantz SR6011
Axiom M5HP, VP160HP, QS8
Sony PS4, surround backs
-Chris