Loads of questions, I don’t count the initial pump run to fill the headspace above the portafilter as part of my shot time, I just count the actual pause time as part of my shot time. However that is for a longest shot so if I pause 8 seconds. I’m probably still going to be doing a 30/32 second shot, so I suppose I make an allowance for the pre infusion..
As far as the high-low flow feature goes if I use low flow I may use a longer initial pump run before the pause because with low-flow, I may not get enough water above the portafilter to do the correct preinfusion I want. If you’re not moving the paddle yes the high and low flow feature can be great you can start off on low flow, increase the initial pump.run of say 5 seconds preinfusion time of 8 shot time of 30 if you want but for the last period of time you can either move into high flow. Or you can do it the other way round and start off with high flow and then move to low flow.
Water will continue to come out of the brew boiler after the pump run has stopped, the brew boiler is it slightly above 100 degrees C because of the offset, and this of course will always bring a little bit more water out of the pro boiler until enough void is created that the outlet pipe is then not covered by water. The pump run after this then fills any void in the boiler, so before thermosiphon won’t stall.