Well, in order to somehow approach Wows economy you need to weight your variables.
For instance, when you're in a certain type of ships you don't have the very same avg time per battle, from what i saw ingame, DD/CA get sinked quicker than CV and BB.
Nonetheless you can also be sinked in 5 minutes, go back to port and take another ship and start battle again, increasing your XP gain per hour.
Another aspect which certainly need to be included in your model, it's the fact that somehow an avg player improves by playing more, increasing both AVG XP and his own survability on seas.
It just can't be linear as you stated in your FP, IMO at this stage we can't really do the maths properly without much datas.
