^I don't doubt the potential, I doubt the value gotten out vs the value left to be had. That's just my approach. The tool is essentially used up just holding on, in real terms. It may deplete in a month if he started seeing less than 3 mile trips, for example.
Non-linear nearly equates to predictably unpredictable, only a reliable guess. Translation: It can go either way, the rate of depletion that is.