+1 on that simple statement! On one of my 30 sized planes, the receiver battery is on one side of the motor box, the ignition battery on the other side and the ignition box is on top of the box. Then, the throttle servo is inside the box just behind the firewall .... zero problems.

Heck, I still have several older planes that fly on 72 MHz. These use a combination of CH and Rcexl ignitions and absolutely no problems with ignition interference and in several cases the ignition box, receiver batteries and throttle servos are all very close together.