How do i prevent a navmesh from curving upwards?

As seen in the picture below when I bake a navmesh that uses a cuboid that is flat on the ground and one that is rotated in the air the navmesh seems to curve upwards rather than lying flat on the surface of the cuboids.

The NavMesh does not need to be flush with the surface that you’re mapping generally. You can use the NavMeshAgent to set the BaseOffset. If you definitely 100% need the surfaces to be as flush as possible, you can lower the voxel size value in your Navigation Bake window, under advanced