Expanding on what I said earlier, fuel upkeep shouldn't effect medium or light tanks. I feel there should be 3 stages of fuel upkeep:
Medium-Heavy:
A moderate penalty for advantaged-but-not-quite-heavy tanks. These include the Kliment Voroshilov and Panther tanks.
Heavy:
A hefty penalty for the standard heavy tanks, this prevents you from fielding too many and helps keep inferior medium tanks relevant by allowing the enemy to replace losses or expand before you call in more heavies.
Super-Heavy:
The highest penalty for the massive Jagdtiger and Tiger II, the penalty on these units will make it difficult to get even a Luchs. Use them wisely.
i dont think having a little fuel upkeep for light vehicles and medium vehicles would hurt.
like 0-1 fuel/min penalty for each light vehicles, 1-2f/m for light tanks, 2-3f/m for medium, 6-7f/m for heavies, and ~10f/m for jagd, isu, kt...