Starving Tara?

The few times that I've left Tara at home alone there's always a surprise waiting for me when I get back. How much milk she's drank in my absence.
I'm never able to pump the amount she's drank (read: been given). Is it unreasonable to presume, dear blog, that we should be able to predict that Tara would consume the amount I can pump out upon my return? Instead she's drank two or three times what she would have, had I nursed her. What gives?
More on this later since my typing (gingerly I might add) is waking her up... and more to come on elimination communication.