Why is navmesh generating through static not walkable?

Goal:
Prevent terrain navmesh from generating near terrain borders.

Attempted:
Created high thick cube walls with colliders around map edge.
Cube walls are set to Navigation Static and Not Walkable.
With and without Nav Mesh Obstacle, with and without Carve.

Problem:
Removed cubes after bake... ignored.... navmesh still there.

Solution?

 

I found the answer. The temporary walls were too high. Apparently navmesh generation ignores gameobjects over a certain height. Bug? So for anyone searching, to exclude areas from baking, place wide short Navigation Static Not Walkable obstacles then remove afterward.