Yup basically the problem I see with a lot of theories people come up with in Airgunning is that they make the mistake of confusing Correlation and Causation
Correlation between two variables doesn't automatically mean that one causes the other.
Global warming has increased since the 1800's and the number of pirates have decreased, but lack of pirates doesn't cause global warming.
I really dislike the "Rifleman's Rule" mainly because of it's name I guess. "Rule" makes it sound like it's some sort of fact - it isn't.
The Rifleman's Rule isn't based on ballistic theory, what it's based on is some big assumptions and geometry.
At best if those assumptions are correct (and they often aren't) then it will give a rough approximation, it will never give an accurate answer.
That's why I made up the "Airgunners Rule of 15's" - hey, if just using the word Rule in "Rifleman's Rule" is enough to make people believe it's a fact, two can play at that game.
The "Airgunners Rule of 15's" is actually based on the correct answers from Ballistic Theory (Exterior Ballistic theory has been around for hundreds of years - it's what the military use to accurately drop bombs on people and although it's still a 'theory' it's pretty damned close to being a fact - ask the Taliban).
The rule of 15's does make some assumptions too though - it assumes a 12fpe .177 air rifle using a reasonably efficient pellet choice and it assumes you're trying to put a pellet into a 15mm killzone. Luckily, for HFT and FT in the UK, those assumptions are ok to use. It's also independent of scope height too, which is another big problem with the Rifleman's rule. Because it's based on Geometry rather than ballistics, it needs to take account of scope height - especially for close range shots, but it doesn't and for that reason it gets the answer very very wrong.