How to zoom a cubemap

I’ve been experimenting with using cubemaps instead of normal scene captures for portals. Currently i’m using this material which i saw in a tutorial:
image
Now, while i know making it entirely match the room being there is impossible, right now the portal shows what feels kind of like an otrographic view because moving closer or further away from an object doesn’t make it project as smaller or bigger.


What i need to know is how to make the material zoom in/out and whether this can make it realistic enough to be used in interior scenes.
ScaleUVsByCenter doesn’t work because it returns a V2.