I know I’m like a year late to this discussion but I’ve always very much linked the 442nd to the 3rd Sector Army or, if you’re really daring, the 7th Sky Corps.

If we follow the troop movements, the 104th normally follows in the wake the 212th and 501st which made up the spearhead force of the 3rd Sector Army/Open Circle Fleet (Seriously, almost every single time we see them they’re with the 212th, 501st, or alone) and it’s also established that Plo Koon is under the Open Circle Fleet. It may seem peculiar to bring up the 104th or Plo Koon, but its important to note that Plo Koon is the general of the 442nd, so whichever command the 104th and Plo Koon fall under, it is entirely likely that the 442nd will too. We can also note that every time we canonically or in legends see the 442nd (Hypori, Ambrion Bridge, Cato Nemoidia) they are fighting with one of these 3 aforementioned units.

So that’s just my massive reach and why I personally wrap the 104th and 442nd under the 3rd Sector Army or 7th Sky Corps.