I'm not sure what type of apically controlled SW you have. The one I installed in my Carden Extra (BME44) is as follows:
SW (with charger harness), fiber optic coupler (A) and battery were installed as close as possible to the engine. The fiber optic cable was ran so that the other fiber optic coupler (B) was installed as far as possible from the engine interference (near the receiver, more than 12" from the spark plug). This device has two fiber optic couplers (or if you want to call them fiber optic repeaters) the fiber optic coupler B is the one that is connected to the receiver channel.
Does this make sens?
Does it match your optic system?
I hop this helps.