Where I grew up, in Bowling Green Ky, everyone seemed to know or think they knew what cross-picking was, and it was always simply the technique of alternating up-down with a flatpick so far as to include moving up or down across strings, or any king of arpeggio. And the wrist was the thing. The arm was considered an error--but I got over that and try to shade the wrist cleanly into arm motion when I need more single-string speed.

Fingerstyle-crosspicking isn't a very good term for the use of open strings for overlapping sustain, it seems to me. It confuses the question. Fingerstyle crosspicking sounds more like Mark Knopfler's thumb-and-finger method, but I'm not sure at what point he begins to use the other fingers.