These days I don't get FOH very often, but my experience of the sound guys I have worked with is positive.
I say hi, have a chat, explain what I'd like, ask them if that's OK, and leave them alone. I don't stress them with many requirements. "Can you make me sound like Duck Dunn, John McVie, or maybe a little Nathan East" usually works. I keep it simple, because they tend to be focused on everyone else anyway!