AM fields do not penetrate the body. The reason is because the soul or the magic-producing organ makes a passive barrier, which is part of the soul itself. The soul is not made of magic, but made of something that makes a natural barrier against anti-magic.
This allows magic to be used inside the body uninterrupted. Creating an AAM field is one of those things. AAM fields are specifically designed to negate the effects of the AM field. The AM field, however, isn't designed to negate the effects of the AAM field, but only magic, even though it still has some effects against the AAM field.
Since the AAM field has already taken place inside the body, it can be expanded outwards, outside the body, and into the AM field. This takes skill to focus something inside your own body, so I would say that only those with magic lvl's 4 and up can do this, but I might be wrong about the scale thing. I know that it would at least require experienced magic users to do this.