NavMesh above than ground

My Terrain (Simple Plane) is at 0 height and y position of the plane mesh is also zero. But every time I Bake it, the resultant NavMesh is a little above than ground, characters are sunk into it upto their shins in Scene Mode. You can already guess what happens in plane mode.

I need to get the characters Down, I can't understand here what's wrong.

Edit: Solved. Just as Jacob elaborated it below.

 

NavMesh is an approximation to the walkable surface - if you need to match the height more precisely use the "Height Mesh" option in the bake settings for navmesh. See http://docs.unity3d.com/Manual/nav-HeightMesh.html

 

Thanks for reply Jacob. That It was definitely the issue. I figured that out, should've modified the question as solved.

 

HeightMesh isnt working for me, it's just a simple cube but for some reason it generates just above the floor and it is breaking everything