I'm not savvy enough to understand your calc's - are you saying the printer aggregates total amount of ink used in print jobs (over a period of time defined by start date to now) and than you can subtract that from the total amount of ink you estimate to be in the maintenance cartridge to calculate the delta which would represent ink used in maintenance and self-cleaning?
Regardless, what I can say, is I have an ipf6100 - the thing has been sitting dormant for at least 3 months (I go in fits and starts) and I wondered if it was cleaning at all (I leave the printer on all the time).
Today I started printing a bunch more - everything is fine.
All to say - the ink levels in this machine barely budge when not in use - I bought about 4 cartridges in January anticipating they would need replacement soon - and they are still sitting in the packaging.
I cannot complain about Canon's ink usage - accepting I have nothing to compare it to, it seems minimal.