Another thing to take into account is pace.
No human mind can focus 100% for more than 20 or 40 minutes (times may vary according to different studies). No matter the figures, it is a fact that racing drivers are humans that cant drive all the race at qualy peace.
Hence, filling the tank for a 100% full pace race distance is a waste.
"You need great passion, because everything you do with great pleasure, you do well." -Juan Manuel Fangio
"I have no idols. I admire work, dedication and competence." -Ayrton Senna