That port/supply thing was brought up in playtesting and I changed how it works so that supply would be pulled from the minor port in that instance, but after a week or so I changed it back because the cure was worse than the problem so to speak. I decided its something to make a note of and when I come up with a better solution I'll implement it.
I asked about this too during playtesting. Ideally, it would be interesting to have some better accounting of actual supply quantities entering specific ports by their unique port capacity (including damage and repairs), actual transportation of supply from those nodes to a subset (automated or designated) of specific units receiving supply from a given port, and over rail/road networks that also account for how much supply can get through. Ideally. But the rules necessary to support all that, the game programming needed, and AI programming too, probably means a game that's an order of magnitude more difficult.
IMHO, this game already challenges players enough to seriously consider their supply capacity for fuel and combat supply, moreso than most other wargames. I think it does pretty well. Sure, it could maybe be better, and as this game system expands to other theaters then maybe better supply accounting will be needed. At the end of the day many players may appreciate being challenged a bit more about logistics, but it shouldn't become so complicated and complex to ruin gameplay. I've been a Bde Asst S-4 and gotten into the weeds of logistics; I don't need to do that again when I play my games.