In my experience, US is among the BEST carriers for NOT doing this. I can recall only once observing a situation where I believe the ground personnel placed two station employees in F (in front of US1s and US2s who were waiting). I see this unfortunate practice all the time at UA -- you may wish to visit the UA threads to read all about this commonplace practice at that airline. Very frustrating and maddening -- caused me to give up UA altogether.