KnowGood wrote:Yes. I use no head space. Final tamp being done by the head. If there is no room for the coffee to move, how can it be disturbed when lifting the lever?

And how can it not be firmly sucked into the screen if it is pressed to it already? Use a finer screen, like the IMS screens?

Even if you could get away with no headroom, the ratio between grounds and espresso would be off with a lever...I rather have some extra headroom than having to do a third (partial) pull which I think carries more 'risk' potential.

But the original question was if you can have too much headroom in a lever...

Think you can, f.e. When you are using a filter basket of the wrong dimensions...like using a triple basket for a double or even a single.
Overall I would imagine, and so far it has not been disproven, that the designers of the lever breed espresso machines design a whole system, or use standardized equipment which in both cases requires certain filter basket dimensions.
For my faemina a 14 g dose really works very well, way less or way more does produce a poor result. I assume the designers know about headroom and how much of it is best, at least in the fifties that seems to be true as the faemina basket is somewhat of a basket case with its typical dimensions, yet it works best with the italian standard 14 g dose for double.

As to the O.P. I do believe you can and it for sure throws the dose/tamp/pre-infusion off balance if the dose is to low. I use a whole range of baskets for different doses so the headspace can be fairly consistent.

Agree with you completely

Thanks, everyone. To summarize my understanding:
An optimal head space is a way to ensure an optimal puck height to match the design intent of espresso machine.

I have been dosing 16g of Hairbender into a Pavoni double basket. The nickel does not leave an impression, although just barely not. I'd suspect 0.5g more will.

To me the roast also should match the design of the equipment...why use a blend/bean/roast you know to cause problems at extraction?
I stay away from certain roast profiles or blends, f.e if I see a recommended dose of 18g of a certain bean I think again because my Faemina works best with a max dose of approx 16 grams ...if I def want that bean or flavor I would need an additional or different machine.

Your theories are all great... when dealing with pump machines. Just try what I say - I have a europiccola I use daily. I grind 14.2g in a porlex hand grinder. Throw it in the double basket, tap on the counter a couple times and LEVEL, not tamp. You require 7mm (or 9mm - can't remember) to sit even with the dispersion screen. I level at 5mm approx. and let the dispersion screen tamp that final 2mm. Dial in the proper grind, try it and then tell me your pump machine method that you use on a lever is better - I bet you can't or won't.

Hehe just tried it...forgot i would need to redial in. As of right now i have an excellent setting and am learning to tweak via tamp..and trying to eliminate some spritzer a that are plaguing me. Been trying minimal wdt, looks like inwill need to study up on improving even controlled extraction.

As of now, pumps home method was superior on my pavoni.