In other words, as I said...the rules exist to make the stories work and don't think to much about it. Read my section on phones.
See the whole notion that Jim puts forth makes no sense for something like the scene in the Van in PG. Here is Harry - in a panic - tossing around magic...and the van works perfectly. And he is inside the van directly above the transmission. Why didn't it lock up?
So my view of this again is don't examine it too closely...there is a whole lotta...it is this way to make this story work.
The rules are not readily apparent without thought, but they exist and while they are mutable, they haven't changed yet in the pages of the stories that I've noticed. This isn't odd to me at all. You have to examine the evidence, both book and woj deductively. uhh let me try it this way.
Wizards effect technology because they are conflicted. that confliction this is what causes machines to break down. Said effect is actually wizards effecting probability, the randomness of luck.
It's contained to machines as even top wizards don't usually put off enough magical aura to do what say, meeting with mother winter would do, but the transfer can happen. Also because they are 'spirit callers' not necessarily of previously living beings but the spirits of the elements themselves, like in GS the ghosts can effect the van but not people. they aren't supposed to, and without manifesting(whih is bad juju) they can't. Wizards can effect people and obects inside others aura's because wizards are mortal, they possess the free will to do so.(technically, ghost can screw with the nautral order too, but notice if either a wizard or ghost do so they tend to go kooky for cosmic reasons)
Now notice when said conflict or belief of conflict fails to come into play, is when they aren't conflicted! guns pointed at Dresden misfire all the time. Dresden himself enjoys blowing out technology, that's prime reason why anything around him would go bonkers, deep down he wants it somewhere. Notice now that NEVER not once has Harry's gun ever misfired? He doesn't want it to! it's very clear cut to me but I might not have explained well enough. however I take great offence to the statement no single theory can explain it, mine can... if only I could explain it lol. Oh, and yea... that's totally an underestimation of jims ability to say they're that way to make the story work. of course they're there to make the story work. But not as silly plot devices that go one way or another depending on what makes the current story. the over arcing story.
I use this connection between magic and random luck to make my own connection between the 3rd fate, the chooser, Nemesis who meets out punishment and literal fortuna, luck. it's all the same thing. Before she was ousted she controlled magic to decide the fate of everything as much as MW destroys and MS is the source of creation.
*Notice milk stopped spoiling and skin conditions desisted as part of the magical effect, right around when people started to learn more about the world and contributing those things to reality based effects instead of bad luck or 'little demons', Ahhh think about it, milk was left out to ward away bad luck! It twas the focus to to be used against it, a talisman if you were. An what happened because of it? Random 'badluck' from wizarding aura's began to accumulate in milk causing it to spoil!