I deliberately forget to tell them...I prefocus using BBF, preset the FL for desired framing, even preset exposure on Manual, and then hand them the camera with suggestion of what part of the background I would like them in capture while retaining us in the frame...they become nothing but an animated remote control.
It increases the chances of getting a desireable shot or two, rather than increased chances of having our heads bullseyed and nothing of the desired background in view!
I love it. An anthropomorphic remote control.
We should all have one.