20 cc is conservative, If I let it run in auto it will eat up to 35cc or 40 cc depending how much ink is left in the lines after retrieval ( I can never get all of the ink in the cart there is always some left in the tubes that will be wasted), What do I do?, I load the ink one tube at a time and stop it when it reaches the head, staring from 4 to 1. Then I also retrieve the ink twice, one in the current/full carts and another one in some empty carts I have, somehow if the carts are emptier ( less pressure) more ink gets inside and less in the tube. when the ink reaches the head I stop it, I do this also for the weakly maintenance. I do the maintenance every 2 days and try to print faded designs at the beginning of each day ( mostly for me, then I can tell if the ink is still keeping it's whiteness or I need to retrieve). It will take almost 3 strong head cleans to get a fairly decent check ( one or 2 nozzles missing) and then I print a batch to get the ink flowing. I would say a strong head clean will use about 1 or 2cc, but I'm just guessing, it is very minimal compared to ink loading, that's why after following wholsaleprint advice on running ink load to get good nozzles I reverted to head cleaning, less ink waste and I get better and consistent results.
would you be willing to post a picture of the inside of your machine mostly interested in the arrangement of the white ink tubes, I think the slope they have might affect how much ink is left on the line when retrieving.