I would note, that in that file I posted, it says,
"If the unit cannot trace this supply line, its supply level will drop by an amount
equal to the number of half days in a turn."
I can attest that this does not happen for me (not sure if that is because of new supply rules, or something else)
but I see several units in my Russo-German scene receiving supply (albeit very slowly) even though they cannot possibly trace that "line of communication" (they are deep behind enemy lines, but still getting some supply--by air? from their hex? A quirk in the scenario design? Not sure.)
Seems like they usually go from, say 7% supply, to about 23% over the course of about 10 turns--not moving, not digging, just stationery. Stationary? Not moving. Maybe that a rule for old ACoW and different now in TOAWIV?