Old Smokey
I have to disagree with you (respecfully... and carefully
)
Finding the real CI requires rocket scientists. It can be very complex to assess the exact operational cost of one flight minute. In addition, the CI will vary depending on each particular route, even in the outbound and inbound sector for a given destination, and depending on the variable price of fuel.
Now, if you tell me that CIs can be easily calculated with a small error margin... Maybe, but even though, most airlines simplify the question too much. They use a fixed CI for every flight, and it remains constant for years, no matter what happens with fuel costs.
In A320, they say that CI 45 cruise MN is approximately equivalent to LR cruise MN. Taking into account that most airlines have CIs well below that, airliners are flying very close to maximum range (CIs of 20, 15 or even 10 fuel Kg worth each minute).