I was on a United P.S. 757 LAX to JFK in C and the plane stopped right before takeoff. The lead FA came to me and asked me to move to F because of W/B. What was interesting to me was that I simply moved from 5a to 3d (essentially one row up) and I'm a pretty small person!
Anyway, I can imagine that even small fluctuations can change the W/B and the P.S. has an unusual configuration, but I was pleasantly surprised nonetheless!