[beate]

Well, the Aptera is two seated and accordingly pretty wide. For an aerodynamic back it might be easier to narrow it horizontally - the vehicle becomes a lot shorter and a lot less prone to side winds (which, btw, is indeed a problem on some velomobiles including the two successors of my vehicle (the Evolution and the Evo-R)).

Furthermore those shapes need to be free standing, i.e. sufficiently distant from the road in order to be effective. That will lead directly to the shape of vehicles like the aptera.

But in the picture of the motorized GoOne You can quite clearly see a major main problem when You want to extend it with some kind of tail: the steep downward angle of the contour.

Another issue might probably be that of outlets for the air from the interior of the vehicle, especially when the canopy is fully open or missing entirely.