Most energy efficient machine - small (e.g. 1gr) but efficient or large (e.g. 3gr) but heat conserving?

Q&A
1

Considering power consumption of identical brand and insulated espresso machines - 1 group and 3 group, minimal daily usage for example. Say 20 shots a day, always 1 espresso at a time, sparsely

Which one would be more energy efficient?

I am very inconclusive, since 1 group machine has to do more heating cycles throughout the day + has a bit more difficult time to recover after a heat loss of espresso shot (small boiler volume + smaller element)

or

is a large 3 group machine better since it would retain heat much easier due to boiler volume and recover very easily and quicker from an espresso?

I am thinking of a ratio of Boiler Volume/Heating Element Power as a variable, but this may just be unnecessary…

2

Additionally

of course we can calculate the amount of energy used for the initial heat-up, or even measure it.
I am wondering how does a fully heated operation compare between machines