Thanks for explaining @tshortt. Excellent explanation. Much appreciated. You’re right, I am getting confused between a fixed range model and a mean range model based on different population groups. It gets very confusing when you try to amalgamate the two to make sense of various models! You end up getting things wrong and misinterpret what is being said. Throw Coggan zones and Seiler zones into the mix and, wowee, you got yourself one heck of a cocktail of confusion. 
I get it now. I think. DrMF is providing fixed values, the 2mmol and 4mmmol values, whereas ISM is moreso providing mean values based on two separate target groups. Would I be right in saying that if you were to follow ISM’s model, you would have to find your own LT1 and then train just below that? Whereas with DrMF he just says to mainly target the Medio range of between 2-3mmol.