Talking with Gaserlake, apparently as long as it's called magic AM fields work against it, period, end of story, no matter what. Apparently, to hear it from him, the only way to deal with it is to use spirit energy combined with magic or an AAM field. Bullshit. Magic isn't designed to do anything until it is commanded. If a mage creates a spell to destroy an AM field, the magic will do it so long as the mage is able to perform said spell.
Another problem is that we haven't even figured out what the hell AM fields are or how they do what they do. All we've decided is that magic can't be used in them. Why? Why can't it be overpowered? Sure, you could destroy it, but if the magic itself is stronger than the AM field, the magic would still win out. It's called brute-forcing something. Yeah, you can pick a lock to get the door open, but you can also brute force it and break it instead. Harder, sure, but faster and you don't need any spiffy tools. Just like shields and AT fields can be brute-forced, so can AM fields. If it can't, then the field is invulnerable and thus godmodding, whether there's ways around it or not.