|I would guess that is correct.|
Did that printer ever give you that information?
I hate to break it to you but I don't think the printer actually measures the ink. I think it uses a counter to tell you when to change tanks. I know at least some work that way.
I really don't know how it could measure the ink. There would need to be a sensor in the ink tank or the tank would need to be accurately weighed.
I suggest you just run the tanks till the finished product is off.