A theory and only that. As a vehicle accelerates the fluids tend to stay put for a moment as the vehicle moves forward. The fluids will gather toward the rear of what ever part of the vehicle contains them. Crankcase oil will collect toward the rear of the engine giving a rear sump pickup an advantage of always having oil to pump thru the engine. A majority of drag cars have a rear mounted fuel tank today and looking at these tanks you will notice the rear of the tank usually has a slight modification with a low spot and inside the tank the fuel pickup is located in this area for the same reason fuel will be their to pump to the engine. A front mounted tank like the picture may offer a similar advantage since the fuel would tend to collect in the rear of the tank and in turn would have a shorter distance to travel to the engine and the force of the acceleration may even help with the transfer of fuel to the engine. This type of fuel tank in these classes of drag racing would generally hold little more than 5 gal. A theory, but also a possibility. This particular tank and it's being mounted in this manor may be just a prop to give an appearance. The size and general shape of the tank resembles fuel tanks I have seen used in drag boats. They would be mounted length wise and sometimes there would be one on each side of the boat.