I would like to insist on my disapproval of not putting sea zones in the West.
The zone would be narrow, but no more narrow than those in the east. All this does is make the Zuma immune to direct assault by sea (as if they needed it anyways), and grant Aurvandil a much greater safety from sea attacks from the North-western realms. I don't think Aurvandil needs such a protection, nor that it is fair.