The Illuminati Motor Works 'Seven' entry for the X-Prize competition illustrates what Hucho's been talking about since the mid-1980s.
If you imagine starting with something like a 1950s Porsche 356,Cd 0.34,and stretch the body out to the rear,you end up with Cd 0.165 according to the Illuminati team.
Had the rear track been narrowed,and the pontoon fenders blended away,the uniform plan-taper would have allowed for even lower drag.