That best for its length tail, L, is 42.5" and that's half my vehicle's overall height, H, 85". (makes sense since D = 2H and L = 1/4 D). This is darn close to the proportion of trailer tails on 18 wheelers (tails vary a bit by brand) since they're the width of one door and doors are half the width of the trailer and the overall width is just barely less than the height (couple inches / 2 doors = inch or so less on each side).
Makes me think .25 L/D might have some significance as the sweet spot for cod reduction/tail length on boxy, bluff bodies.
http://www.palmerleasing.com/images/53_closed_van.png
http://www.part20.eu/en/applications/trailer/
Since that's my overall height from the ground, not just lowest point to highest, I think 42.5" is probably actually longer than would be proportional to a semi van trailer. If my back bumper is 10" above ground, half that is 5", and .25D shrinks to 37.5". Better go measure...
Rear bumper is 19.5" from ground. Half is 8.25, 42.5 - 8.25 = 34.25" for L. Dang now I want to lower the van...NOT happening