my sideline is notorious for having 7 assistant coaches standing right on the sidelines during play. HC says to me: "But you're supposed to be on the field, right? You stay on the field and we can stay right here [points to restricted area]."
I hope he was smiling when he said that. I don't think anybody has trouble with a coach who gets caught up in the excitement of the game and wanders where he shouldn't be, if when corrected he acknowledges and steps back where he belongs.
On the other hand, a coach who seriously suggests the other side of the line belongs to him, might need a thorough explanation of the rule followed by vigorous and precise enforcement, for him and ALL his assistants.