Thanks for the replies.
My understanding of electricity is pretty superficial. I take your point about only grounding the shield at the mag. If the two wires are at 90 degrees will there be a pulse induced in the headset wire?
On a related theme, I'm trying to find an acceptable location in my panel for a whisky compass. My preferred spot is above my SL40, but I thought it would get too much influence from the radio. Sitting right on top of the radio there was about a 15 deg. swing during transmission. If I sat it on a piece of 1/2" plywood the swing was reduced to 2-3 degrees. Pretty surprising.
So now I'm wondering if, in the p lead case, 1 1/2 or 2" separation might be enough. I know I'm comparing apples to pomegranates.