The ratio of the work being put out (heavy attack) to the work being put in (consumed combo counter) is the efficiency of the heavy attack. The inverse of this can be considered the efficiency of consumption. So, increasing consumption efficiency decreases heavy attack efficiency, and vice versa. Mods like Focus Energy (despite their terribly worded descriptions) reduce the amount of the combo counter needed to be consumed for a heavy attack, which is an increase in heavy attack efficiency, and thus a decrease in consumption efficiency.
However, I'm not totally sure efficiency is the correct terminology to use here, at least in regards to consumption. So to reduce confusion I'll probably just get rid of the efficiency idea all together.