I've played around with a lot of different mic positions. The one that is the closest to what I hear when I'm playing a 12-string is spaced omni mics, one at the join of the neck, one at the tail, both rather close.
Maybe just because it's a giant jangle of different noises coming from all directions, but that's what I hear.
An example: Slow Blues in A
|Dance, a Portrait of Tom O'Leary, c. 1980 Art Sulger|