skylark - I think this is becoming way too complicated when it needn’t be :-)
You pour a double espresso (i.e.: a 1:2 ratio, e.g.: 18g in, 36g out, or 20g in, 40g out) into a cup.
You then add water (dilute) to your taste. I don’t drink Americano, or long blacks. The idea is that you can then say things in relation to the espresso shot in your cup, e.g.: 1 part espresso, 3 parts water) (so that would be, with the base of a 40g espresso shot, a drink which would yield a total of 160g (120g of water on top of a 40g espresso shot). At this level, you can use “g” and “ml” interchangeably, so a 160ml drink.
Dilute according to taste, and don’t worry about the cup size too much. 👍