Interference and servo position varies with the installation.

I've installed the throttle servo only an inch behind the engine and only a couple more away from the ignition without any problems at all. Care was taken to eliminate any conductivity sources and higher end products were used, so maybe that helped. There are others that have had nothing but problems even when they had 12" between the major components.

It all comes down to using your head, using good products, eliminating any metal to metal contacts, making sure everything is tight and won't loosen up, and some good range checks before the first flight. Engine off and engine running. Don't use a PCM receiver when doing the initial range checks. Change to PCM only after you have determined that all is well.