in case you were wondering, there are usually a number of ways to extract a coffee i think, rather than a singular optimum
for example, with this coffee if you prefer more fruit acidity keep the dose at 20g, keep the grind setting the same as before, but dial the pre-infusion pressure back to 1.8 bar
the cooler brew water reduces the extent of the extraction from the coffee in two ways; first the cooler water itself (every 10C movement in temperature halves(reduction in temp)/doubles(increase in temp) the rate of reaction), and secondly the cooler water is absorbed by the coffee grounds to a much less extent so the flow rate through the coffee is higher and therefore the pressure at which the extraction occurs is also reduced - the extraction time is perhaps just one third of the extraction time when the pre-infusion pressure is 2.7 bar as a result, which as you would expect produces an espresso that tastes completely different from the one where PI=2.7 bar
the key principle in espresso is equilibrium and that is why the machines we have designed for you are so forgiving - when you alter one parameter other parameters automatically move in the right direction to help you, preventing you from moving variables in directions that conflict with each other. for example, if you have a light roast it is less soluble than a darker roast. to counter the reduced solubility of the lighter roast you increase the pre-infusion pressure. but the design of a londinium espresso machine means an increase in pre-infusion pressure also gives you an increase in brew temperature AND an increase in brew volume: all the parameters are moving in the right direction to ensure you achieve an optimal extraction from the lighter roast. the opposite is true when you are using a darker roast.