Revit :: Controlling Contour Lines

I have a small residential project with corner lot sloping up diagonally from the intersection. The client wants to raise 'usable' surface of the site by introducing terracing - 3 retaining walls 3' high and 3' apart.

All is interrupted by a driveway and series of steps leading to the main level. I'm trying to modify existing surface, but the topo seems to have 'life of it's own' . I've tried to Split some surfaces to make life easier. That worked to some extent. How to make the topography cooperate? Is there a way to 'turn off' triangulation? ( not the visibility ) . I'm certain the contours I'm creating can be built, but Revit is 'changing' them to something else. Some points that I place are simply ignored.