I'm sure there's lots of tradition behind the name Sylea. It might be the "informal" name of Capital, or maybe it's used to refer to the seat of government as opposed to the world itself... "Sylea wants things this way" is the same as saying "the Imperial government wants things this way", perhaps, and "Our trade lines extend all the way to Capital" is how folks refer to the physical world.
No real evidence of this, it just feels that way to me.