Quick question from a WH noob

Hey there

I‘ve been playing WH3 as the empire (immortal empires campaign) and I came up with my own narrative that I have to go out on a expedition to the north to help my human fellas from kislev out against the forces of chaos. (I played the prologue campaign)

However I noticed, that the starting positions of the chaos factions are quite different than in the realms of chaos campaign, being spread out everywhere.

Is there something I‘m missing? I thought I can get „into“ the chaos realm somewhere up north, I‘m a noob lore-wise…

Is my campaign narrative even possible?