Unregistered, I'm not an engineer so I can find proofs for one or other opinion only with the tests made by privates and brands. But It's not me the one that have just told that Mercedes made a test and found the better way was the "classical", I'm surprised a bit you consider this not relevant, especially seeing how Mercedes and other german car brands are considered there in Usa (I'm not german, I'm italian).
So pheraphs mine are not proofs like the Mercedes one, but they are added elements to talk about the problem. But If none between NP and other brands have considered the other way of carrying the boards there should be a reason, don't you agree?
I must confess that mostly I go windsurfing alone with two boards lying inside the car beside me, so I don't carry boards outside too much, only when travelling with my girlfriend. As far as I can remember I've tried some time the not-classical way, without feeling relevant differences, and pheraphs a little loss of speed; but I'll try again, having nothing to loose as my boards (Score) are old, so not much value to risk.
The classical system anyway has big advantages for sure with a board with daggerboard, as this last can easily fall down on the car roof if board is carried stern forward and hull down, so for sure I'd avoid to suggest the other way to all beginners and raceboarders; hey, this is a Nico's original idea! So at least in this I'm a thinker not a follower!!
(BTW a 44 years male, with C6-C7 ernia but still windsurfing (33 times from 1st of April) and snowboarding in winter, with 8 various windsurf boards, who dared to go alone in Munchen and buy an out of time 460 cm board called Serenity and carry home in his town, being pheraphs the only or one of two owner of this crazy marvellous board in Italy ; windsurfing (also) in Venice watertown where he use to go out and rig over the water surface in shallow waters unloading the board from a boat; and also who madly travels in summer north to Denmark to look for real even if colder summer winds instead staying in quiet sunny beaches of Italy (being "the only italian to go windsurfing north in Denmark" as told me kidding mr. Keppler in Pforzheim); so all these things seems coming from a follower or a thinker?)