No direct experience with the white box, but I do use other stoves. It seems that by the time the stove has cooled to the point that you can salvage the unburned fuel that most has evaporated.

I think the practical answer is carry more fuel than you need until you get good at pouring the right amount.
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"In theory, theory and practice are the same. In practice, they are not."
Yogi Berra