I don't think that most rifles are less accurate at longer distances.

Some are but many are not. That's a factor of velocity and pellet. I do think that reliable accuracy ends somewhere after 60 yds for most airguns but that's because of what they are. A light pellet at low velocity. Eventually, things just go bad. Pick a heavier pellet and push it a little faster and you've a totally different outcome.

I personally like the Troyer Factor because it is easy to understand and helps in setting up a course of fire without over burdening the match director.

The whole purpose of the original posting was to make the point that we can't assume that an identical course rating will let us compare two different matches. A 30 Troyer rating on a course with predominantly longer shots will probably score higher than a 30 Troyer rated course shot at closer ranges.
John