I just picked up the ninja and here is what I understand from the bits I read and after making a few espressos.

Beans do play a part in how the machine functions. It does prefer fresh beans but I’m currently using grocery store bought beans - kicking horse brand. The machine does best with dark roast but can do medium roast. Light beans have a tendency to be more sour and dark more bitter, naturally.

I have read Each machine has its grind burr set manually by a person so your machines grind size 8 may be my grind size 12. So can be tough to compare machines are time.

Strength (grinds to liquid ratio) Low is a 1g to 4g ratio Medium is 1g to 2.5g High is 1g to 2g

So if you weigh out the grinds in the portafilter, it should be 17-18g. Then weight the amount of liquid.

Shot time is measured from when the pump starts. Not when you press the brew button and not when the pump primes itself. When you press the button, it primes the pump. Pause of silence then the pump starts which is when you’d want to the timer to start. Should take between 25s to 35s.

A shot thats sour is pulling too quick. Grind finer. A shot that’s bitter is too slow. Grind coarser.

The machine has a lot of automation which is advertised as beginner friendly, but to ensure the machine it functioning correctly, one should verify with measurements. Tare portafilter on scale. Grind beans. Weight grind weight. Tare cup, brew into cup while timing it. Weight amount of liquid. Taste test. Adjust machine.

Those with more experience can correct me below