My own case is the VW Beetle body. I like it because the body begins it's plan taper at the door edge, rather than the rear axle line. I have established by physical measurements what is shown in the rendering—the side taper meets 3 feet behind the rear valance. The top taper meets the ground at a distance equal to the wheelbase. The fender-skirts are a different matter.
Here's another picture with a truncated boattail and a high-tailed stinger:
The big 18-wheelers are an edge case because the Fineness Ratio, or length of the body, is so great all the streamlines are straight front to back. On shorter vehicles air is creeping up the sides with two counterrotating vortexes springing over the edge and onto the roof. If the sides taper and the roof is flat, the air rolls off the top onto the sides.