Ah Bob, I’m working on the basis that if Simon travelled 27 miles and climbed 1900ft then he also descended 1900ft within those 27 miles and, assuming there were no flat bits, and all gradients were equal the real climbing would be 1900ft in 13.5 miles. He used basic maths to divide ascent by miles so using the same maths he could claim 140ft/mile. I was trying to make him feel better!
Of course, he could have ridden 26 miles at a steady gradient and 1 mile off a cliff which is why your figures are the correct method ;-)
Personally, I find continuous level riding the most tiring. No descents to recover from the climbs, just continuous pedalling with no relief.