See rule number tree in my previous post. Rephrasing that rule to omit dB: Signals are reduced in strength by the inverse cube of the distance. Meaning, that when a servo is 16"away, its radiation level is 1/16th of the servo placed at 4"distance radiation power level is:
(4/16)^2=0.0625 times. Quite a large reduction, giving the transmitter signal a fighting chance.

I do not know why some plane builders do not care where that nearest servo or receiver connected lead is.
I do know, that Engine and ignition manufacturers advocate as large a distance as is feasible.
From my own background and limited knowledge, I am very much biased to believe the ignition/engine manufacturers. There always will be exceptions to the rule, but that does not change best practice.