Well, I'm frozen, 20 degrees out and prop wash on the hands is a bear. Anyway, I get interference from all side of the plane, front, rear, and sides with the antenna inside the fuselage and outside attached to the fin. However, I did notice something, the interference is affected by the location of the radio. Standing in a given spot where the interference is real active, moving the radio a couple of feet up, down, sideways will stop the interference.
That is pretty normal with an interference problem. However, you need to be interference free at least 150' in any direction from the plane with a collapsed transmitter antenna.

From the side of the fuselage, the radio has a clear view of the antenna without the flying wires blocking the signal. Any comments on this?
The flying wires don't in any way shield the antenna at the frequencies (72 or 50 mhz) that we use for our planes. If you were using 2.4 Ghz this might be a different answer. My Jungmeister has flying wires, landing wires, and brace wires all over it and there is no sign of interference. Not to mention a big landing gear wire set.

You need to, once in for all, determine if the interference is ignition related or vibration related or........

You can temporarily shield the complete ignition wire with a piece of aluminum foil wadded around the wire and cap. Ground the foil to the plug with a clamp or tie wrap. Are you using a resistor plug such as a Champion RCJ-7Y?