Very astute explanation.
However there's a point at which if you broke the proration to the very minimum, Daifunka/Ashura might be more. Daifunka does ~1100 minimum, add 20% you get ~1350, whereas Daifunka ashura should net ~ 1600 in that same circumstance. However daifunka in a less prorated scenario usually hits 2k+, making 20% 400+, and the ender of daifunka prorates to shit so ashura is still probably going to be minimum.
So in actuality, you're more likely to get better damage from daifunka/ashura on longer combos, and more from FRKZ/Daifunka on very short ones. But FRKZ daifunka is always clutch as hell.