ON my first gasser, I didn't obey the "separation" rules and had mounted a kill-switch and throttle servo on the firewall, with no isolation. ALWAYS had reduced range, but never figured out why.

For your CG issue, the RX battery CAN go all the way back to the rudder post, if you need to, and move the RX back there, too! The idea is to Absolutely, Positively, keep the ignition battery and any ignition related electrical stuff in front of the firewall, and minimum of 12-16" from ANY Rx related cables, harnesses, antennas, switches, etc.

We may not like it, and I ignored it - ONCE - and won't again.
If I can't get appropriate separation I choose a bigger airplane.