Jeff, my compass is about 1" from the intercom(pm1000) and does not cause a swing in the heading. Transmitting on a comm radio does cause about a 10 degree swing in my set up. That doesn't matter too much to me since it is a brief and occasional thing. I experimented quite a bit with compass position but in the end had to compromise. I only pplan to use the whisky compass if my Dynon fails! Would not have installed it at all but my Canadian inspector requires one.
Good luck.