You can't put the EDC near any cable that's carrying much current. Since the battery has high current wires, you want to stay well clear of them, about 2 feet away or more.
I have my RV-8 EDC under the empenage fairing, and the only problem I'm going to have is the white position light wires. They run within about 6 inches of the EDC, and cause the heading to change about 3 degrees when I turn the light on. Fortunately, I won't turn the light on often. Strobes don't seem to cause a problem at all.
Stationary steel objects should be avoided, but it's difficult to get completely away from anything steel. A few bolts in the vicinity don't seem to be too much of a problem.
Moving steel is a much bigger issue. You want to avoid being near that. The control stick really messes up my compass when I move the elevator. Fortunately, it's pretty accurate when the elevator is neutral, which is where it will be most of the time. When maneuvering, you can't expect a real compass to work anyway.
BTW, Dynon usually suggests holding a cheap compass in the areas you are thinking about putting the EDC. If it's affected by the current, or steel around it, then your EDC will be too.
Cheers,
Rusty