I have no saying. I'm a decent pace line guy, as I do the obligatory motions for objects, hazards etc.
I do not say "car back." I simply expect people to ride on the side of the lane.

When people used to say "car back" I would often ask "when is there not?" but most cyclist didn't get it.
Now, I just shut up, but think "of course, it's a highway; there is always a car back."