LONDINIUM-R double shot videos

Some forum pals asked me for confirmation on the 'shot volume' of the LONDINIUM-R. 

The shot volume in itself is irrelevant, but what it indicates is the initial pressure of the shot. If the lever is catching low, that means extraction, pushing out the espresso starts at a higher spring pressure, and therefore the higher overall pressure profile of the shot if you use it for the first 30g of espresso (and let the rest flow away into the drip tray). 

The adjustable consistent pre-infusion pressure of the LONDINIUM-R allows you to find and select the pressure profile (and in consequence also the temperature profile) of your personal taste preference.

What determines the shot volume with a lever machine?   

There is a pocket of air above the puck: between the puck & the shower screen and above that between the shower screen and the bottom of the piston. The piston is first moved up and a little more air is sucked in through the puck. Then water splashes in and rains through the shower screen, on the puck. When the lever is all the way down and the piston all the way up, the brew chamber is filled to the max. What is the max depends on the pre-infusion pressure at that time. 

At 1.3 bar boiler pressure (the first Londinium that I had) this is less water than at 3.5 bar because at the much higher pressure more water fits in as the pocket of air can be more compressed. Then the lever is raised again and the spring starts to work at a higher, more compressed point than when there was a lower pre-infusion pressure. So at the higher starting pressure, the extraction has more water to press through and also more power to press it with, so it has a longer 'breath' like a trumper player who is able to sustain blowing his horn longer than the other guy...