A few thoughts
Banooma - it's good that you've read the instructions (my wife always accuses me of bypassing them but I usually get around to it eventually!), and that you're concerned about deviation.
One thought is you can contact the manufacturer's help line and hear if they can elaborate on it. My guess is, if they're smart, they won't open the company to liability but they might provide some interesting insight. Just for giggles, you might ask them what kind of compass sensitivity the 3-ft recommendation is based on.
Another thought is, it depends on the quality and condition of your compass. If it's an OEM unit, a really old hummer and never been serviced, and if you never really use it, then it's basically just for show and doesn't really matter. Well, except, perhaps, for resale. But then if a prospective buyer isn't savvy and doesn't plan to use it then it still doesn't matter.
Then, there is my lesson learned.
I installed a loud hailer and bought the remote speaker-mic with push-to-talk. The main unit was installed at the nav station down below where it's hard to get to from the cockpit so, hence, the remote.
The next step was to install the remote speaker-mic. That's one of those small units about the size of those hockey-puck type mic units like on CBs, and the speaker is about 2", max. I checked out it's sensitivity to my compass, a Wheems & Plath "Venus" and, lo and behold, I had to have the darn thing about 5 FEET
away to avoid moving the compass card!!! And that's not all - that was with it not even connected. Plus (or minus, depending on how you look at it), it only has a quite small permanent magnet!
Okay, so now you wonder about all that other stuff, you know, like stereo speakers with 20 oz magnets, VHFs (with speaker magnets and mics), etc., and you have to really wonder what the value of the compass really is.
Another example, and it's easy to check, all those who have had problems with their autopilot. There have been a lot of posts about these problems. A lot of these issues can be traced back to magnetic interference of one sort or another.
I've participated on a few "Power squadron 'races'", this is where they go time and distance so it's not exactly a race, as an observer and you'd be surprised how loaded down the bridge is on some of the power boats with electronics, gauges, and who knows what else, and they have a compass sitting there right in front of the wheel. So impressive. I guess.
Checking by swinging now may reveal no problem but if the compass is ever upgraded (or repaired) then it could be an issue.
On a more positive note, I'm sure the manufacturer of the unit has done everything possible to minimize the electromagnetic radiation so their 3-ft recommendation SHOULD BE a valid one.
