Oristocorys Castle's location only makes sense if there is naval movement in the game, to provide some sort of naval base for transports going from Zeonica to Ortysia. If you think about it, Jalmarys is in the heart of imperial lands, so there's no real reason to keep a large fortress by the river, especially when the enemy would have to push through Garontar/Ortysia from the south and Lageta/Hertogea/Rhotae in the west. But without naval transportation in the game, yeah, Oristocorys should be further north by Vinela.
Poros is in a mindboggling location. I get it, it was probably a castle originally to protect the grassland villages, then got larger as it protected trade moving west. Buuuuut, there's this annoying valley pass just north of it making its trade protection useless, so you may as well move it to be just southeast of Canoros, so it would've been overseeing trade in the valley and east/west. I get why there's the cluster of Vostrum/Lavenia/Danustica/Odrysa to prevent an Aserai steamroll, but if the devs don't move Vostrum to the mouth of the river to its west you may as well move Poros nearby.
Since the game lore has the Khuzait taking the eastern province from the empire, I'm kind of thinking the empire started at Phycaon, which means if you have a capital city upriver, you're most likely going to have a city at the mouth of the river to protect/get rich off of trade going upstream. Poros or Vostrum should really go there.
Another big nit-pick of mine is Argoron. Why is it there? Like, at all? There's this big ol' island and it's not a port city, but...a river one? But wait, if you look closely that river doesn't end nicely, but rather with rapids. Who in their right mind would build a city there, let alone who would live there? I get the balance reasons to keep the city focused to protect Amprela, so I think the easiest thing to do is move the rapids to the south part of the island so Argoron can be a river port city.