Don't stick stuff in there that irritates, or you'll have a pain in the neck for sure. 1" 23-25g seems fine, the traps are really dense so you feel that pin going in the whole way like no other muscle. Since its so close to your head its almost like you hear it tearing its way in.
Kind of tough to reach but the shots are fine if the gear is good, I've done it a number of times when doing frequent shots.
I go in about upper-center, and upward meaning not in a rear trap for example.