I am not privy to any such equation-rather it was an oblique way of saying that you can construct a ratio using any variables to better understand what costs actually are on a unit basis.
Broadly divide the entire flight crew overhead by the number of passengers (multiplied by a qualifier such as distance, time or any other variable which provides the dimensioning insight.
RPKs are the industry standard, but obviously they do not provide a picture of costs on an hourly basis.
Any such pay calculation would have many issues to address. At the end of the day no pilot that I know would accept more financial risk for the current reward.
In any event the way that pay is calculated is moot: there will always be a perception problem that can be manipulated by rhetoric.
An (apparently low) pay per passenger number would only serve to make our pay seem like a bargain. It was a throw-away line on my part, but it could be a tool for educating the travelling public.