I've gone to a single wire from bars to frame.
I will use the junction box in the bar end or under the saddle.
Wires can be in any order. Too many variations, but much cleaner front end.

This one uses that coupling via the stem for all internal wiring. JBox is under the seat.
Venge Di2 Wires.jpg

This one uses the bar end J box - see left HB end. I wired this before the 9100 box came out. I now use the current flush bar end box. I also use it on a TT bike.
MASI Di2 2.png

~12.3 lbs here and not lacking any stiffness. Got it under 12 lbs now using a 1X.
MASI Di2.jpg