Im not radio smart enough to know the reasons,but electronic ignitions seem more likely to cause interference than flywheel and coil setups,and you must be much more careful about seperation with the electronic type.On my first CH equipped gas model I did all the right things but for some reason I mounted the two on/off switches side by side......and instant hit was the result.
CH sell Bosche caps to which you solder the ground wire from the plug lead.These work very well but are large and very ugly.Im going to try to find out where the ZDZ caps and armoured leads are made and try to adapt one to one of my weeder conversions with a CH ignition.I use weeders in 1.20 sized models and the smaller neater cap would be a real help for more sightly installations.......