I need to extrude a boss off of a surface that was created using a revolve. I have two versions of this part. One is with the outer surfaces parallel to the top surface. The other is at a 1.5 degree taper. I can create the boss in part one but not in part 2.

Why can't I use any of the surfaces with a 1.5 degree taper in XG21289R4-molding? I tried creating a plane using vertexes but the feature is still not right.