Anyway, I'll repeat - incident at half way i.e. equi-distant between the two officials? Who's call is it? See it's a nonsense situation to have two refs.
Easy. If Ref 1 is in charge of the goal end of the side of the pitch to your left then it is Ref 2. If at the other end of the pitch then its ref 1. Basic ref/umpire mechanics as used in basketball and other sports that use multiple refs. I've experienced it 1st hand and even umpired games using it and it works...as crazy as it sounds.
Open your mind...look into my eyes...1-2-3
That's exactly why Platini's NFL style "endzone" ref assistants would work better. There's still just one ref, but effectively 4 linesmen, but the two endzone linesman are specifically charged with foul play within the penalty area.