tompoland my understanding Tom is that the probe is checking the temperature of the coffee slurry, and adjusting incoming water temperature in all profiles to ensure this matches the desired puck temperature. I agree there is a detectable difference in taste in shots pulled at a profile specifying 90’C when compared to 93’C. I don’t believe however a cooler portafilter causes a large problem here as this is compensated for by the incoming water temperature of the DE1.
The thermometer is not able to measure temperature at the bottom of the puck, but unless we leave the ground coffee in the machine to completely warm to group level (I suspect this may not be desirable or even possible to raise it to 93’C in a naked PF!), this is an issue which applies across all machines, even if the PF is hot when the shot starts.