Issues with using Corridor Extents as Surface Boundary

While teaching recently a Civil 3D 2013 class we came upon an interesting dilemma with Corridor Surfaces.  When trying to constrain a Corridor surface using the corridor itself is now always presented as an option by default.  It may not always be to our advantage.

The issue is evident when the a subbase extends further out than the proposed TOP surface.  When trying to constrain the proposed TOP surface with the Corridor Extents, the surface will go further out than the Daylight.

The fix here is to constrain the surface using Add Automatically using Daylight or Add From a Polygon.