I had a RFI problem with my G45 w/CH ignition in my Christen Eagle.
I installed a Bosch cap and had lots of separation between the ignition system and the airborne radio system.
I finally troubleshot it to a new futaba rx that had bad noise rejection. The second new futaba rx was the same.
I installed a Hitec Supreme and the problem went away.
It's been good ever since.

My next RFI problem was with my ZDZ40 equipped Texas Hurricane.
After much troubleshooting, I traced it to a bad throttle servo.
I installed a new servo and the problem went away.
I now have a free Futaba S3003 servo for anyone who will pay for postage!!!!

I will mount throttle servos fwd of the firewall if the engine has a fully shielded ignition system.
I am careful of the unshielded components.....switch harness, battery, and associated wiring as I believe that they emit some RFI.

Thanks
John