that's a lot of math to say something pretty simple... lol. I've not heard anyone ever say that the gain remains equal throughout every change.
Did you know on a 440, that the gain from going from a 3 hp lawn mower air filter to a 14x2" air filter is greater than going from a 14x2" to a 14x3" air filter? Once you go from the lawn mower air filter to the 14", the gains will not be the same even if you stack three 14" air filters on top each other. The % of change dwindles.