Why they use so much de-icing fluid

[pelmet]

I thought they were just doing it and didn't care or charging the airline extra but(and I'm sure you already know) it turns out that the extra fluid is strictly for the head to enhance anti-icing capability....

"To use Type I Holdover Times Guidelines in all conditions including active frost, an additional minimum of 1 litre/m2 (~2 gal./100 sq. ft.) of heated Type I fluid mixture must be applied to the surfaces after all frozen contamination is removed. This application is necessary to heat the surfaces, as heat contributes significantly to the Type I fluid holdover times. The required protection can be provided using a 1-step method by applying more fluid than is strictly needed to just remove all of the frozen contamination (the same additional amount stated above is required)."