People have a lot of opinions on this. General practice is to keep anything connected to the engine as far away as possible from your radio, and that includes kill switches, charge jacks, batteries, wires, etc.. I've seen some magazine articles where the author has placed the throttle servo on the firewall next to the engine. All I can tell you is that in my latest plane, a Yak 55, I've had to place my receiver and rx battery pack at the very rear of the radio compartment, and have the engine switch and charge jack at the very front, giving me about 12-15" of separation. On tests, just having the charge plug dangling in the radio compartment reduced my range significantly. My throttle servo, connected via a nyrod, is about 12" away from the engine ( I had started with it about 8"). The bottom line is that each installation has variables, such as the condition of the spark plug lead, type of plug, ignition system, magneto, etc.. You just need to install it how you like (without cutting holes I'd suggest) and then test the range. If you have a signifcant drop in range, depending upon your radio manufacturer's recommendations, then try moving the components.
Hope that helps.
Sam