3 man lock down position question

[stewcall]

NFHS
My first 3 man scrimmage last night. Really liked 3 man (person)Besides missing a flex as the trail I held my own.

With less than 1 min. our board likes to lock the C opposite the table. I noticed the other 3 officials (we had a 6 person crew to do 8 quarters)were confused when the locked down. The confusion occurred when the ball went out of bounds on the the C's sideline. I understand this should be discussed in pregame, but my question is how do most officials like to handle this. The simplest way it seems to me is to let the C handle the throwin and remain in lock Down no matter what direction. Your thoughts