RE: [OR] Site Grading -> Building A New Breakline Feature from A Feature Created by a Linear Template or Corridor

I am trying to create a new 3D element by a slope from an existing 3D feature representing a back of curb that was created from a linear template or corridor. The target is a 2D element representing the back of sidewalk. In some areas, the target represents a wall. In other areas, there is another back of curb that will be my sidewalk limit. When all of the 3D elements are created, I will make a terrain object representing the sidewalk area and apply a sidewalk paving section.

Nothing I have tried has allowed me to use any slope from 3D element tool.