Preventative officiating!
Letting Team A line up with their feet 6 yards behind the restraining line and not calling it: Bad
Flagging it and taking back a game-changing onside kick miracle because of what is, let's face it, a somewhat technical rule: Also bad
Hollering at them and getting them to comply with the rule before it's kicked: Much better
Also, let's not be too technical about how the rule says "none of the kicker's teammates can EVER be >5 yards back AT ANY TIME before the kick." If they're lined up like this and you warn them and they move up, let them, I don't care if the RFP already happened. Likewise, when a team breaks a huddle before a normal everyday kickoff, and they spread out to their positions, if one of them takes an arcing route to his position and he happens to travel to the A-29 along the way, I got nothing as long as he comes to a stop and it's not part of his actual run-up.