If you want to define a complex bend like this you need to define it through three separate bends: Two part that only bend horizontally and the center part that bends in a different bend plane.
Defining the polygon points for these bend parts is not trivial. Furthermore, we are not sure whether this complex bend is actually possible (without kinks between parts of the bend).
Our approach would be to approximate this situation by using a single bend with the combined bend radius of Rc.