AutoCAD Civil 3D :: Corridor Datum To Follow Protruding Surfaces

Am trying to create a corridor datum surface that goes around Protruding lanes but it seems I am Short on knowledge here. the outer lane, LaneOutSideSuper has a greater thickness than the inner lane (same sub assembly) and I would like my datum surface (actually, not only the datum surface but other layer surfaces) to attach its self around the bottom links of both surfaces but it shoots from the Crown_sub to the outer lane Datum.

I have used the bottom links overhang and adding feature lines to the surfaces but it doesn't seem to cut it. Attached is an illustration of the section view. The top figure is what I hope to get and below is what i seem to get.