What they said.
I run omnis from the front row or as close as I can get, usually small theaters, churches, or halls with quiet 'jazz' audiences. Get up close, on stage if you can. I like running omnis for this type of stuff because even if I can't get a super present up close sound from some instruments (often piano), if the room is decent and the crowd respectful, the sense of ambience and depth is superb and often more natural sounding to me than having all the instruments up front, super clear and 'in your face'. It can be quite nice to have, say, the sax sound up front and the piano a little deeper in the soundstage. All depends on how you like you jazz to sound.
-edit
a few things I've recorded recently have the soloist standing at the front lip of the stage sometimes, almost in my lap in the front row. In this case 'on stage' would have been too close, behind or under the soloist even, but generally proximity is your friend with acoustic shows, IME.