I know everywhere will be different, but is there some rule of thumb when going into the realm of 'large' drinks?
For example, a latte basically being 60ml espresso, 120ml milk and foam top and cappuccino being 60ml espresso, 60ml milk and 60ml foam. Which ingredient/s is/are increased to take the drink to a large?
60ml? +120 milk is going to be a very strong latte unless you are under extracting.
Anyway regardless, ingredients should be increased proportionally as the total volume increases to maintain consistency of strength. So if your large coffee has twice as much milk then you ought to put twice as much espresso in it.