Aha, I see. So amount of IC is what matters. What about production efficiency?
No, that tech is for improving the speed of production.
The fuel you get per day doesn't have anything to do with production. It's something the AI does by itself for you. It looks at what your industrial capacity is and makes some sweet conversions for you. For example: it converts a portion of your coal (energy) to oil and it also converts a portion of your oil stockpile to fuel.
What country are you playing with? There are only few countries that can have a lot of armoured divisions.