it depends on the bean, how old it is, the humidity, your machine etc. It'll be hard/impossible to get a great espresso shot from a lot of machines as they just don't have the power. Compound that with the quality of grinder.

Some beans are very forgiving and give a decent espresso with a wide range of parameters. Some beans are very picky on getting the settings right.

I've had a range of machines - and my current machine is the only one that I can get a decent cup from (BES920).

To your question, you need to adjust depending on the output from your machine.

I see. But you basically only tweak grind fineness and amount per cup? or does your machine lets you adjust other parameters?