Well Sean, you did indeed squelch my first suggestion! See if you can eliminate pi_s poor antenna routing by using a non-conductive rod (a wood dowel perhaps) to put the antenna vertical, as in a full length whip, and placed away from ECU, batteries, servos, etc.

I would not think the issue is with the FADEC. I have never had any radio issue with them with the MPX 12 channel stuff. Always a chance that you got a bad one that is bleeding some weird RF. Can you increase the range by unplugging the ECU?