A word to the wise, these armies generally stay put, but sometimes when a faction attacks one of them they will all start attacking aggressively. This happend in one of my romani games where i attacked some of the rebels armies around Iuvavoaeta, the rest (about 10+) went beserk and started attacking every faction bordering the province.

I'm guessing the reason Gintaras-Ostan has less stacks is because its right next to the Sweboz who are indoubtabley attacking it constantly