dr gary, I like your use of logging software and congratulations on a successful Scace-lite. Mine needs something to seal the wire to the thermocouple within the hole so that water doesn't escape through during pre-infusion.
If you use the same grind setting but decrease the dose by 2-3 grams the water will more thoroughly saturate the puck during preinfusion and the shot's duration will decline. Will the temperature curve over ~30 sec extraction hold that shape?
I want to call attention to the useful diagram emils posted earlier:
Is there a point on the outside of the group, the temperature of which equals the temperature of the water that initially enters the coffee bed? (Your measurements suggests 198 F with your current pressure setting.) The idea that there is some water in the path to the group in steady state with group and boiler prior to pulling down the lever suggests to me that there might be such a point.
EDIT: I have a probe on the bell so I know when the group reaches steady state temp of ~77C. (boiler cycles between 1.0 and .85 bar. I added a thermocouple probe and measured behind the group on the chromed brass below that ball-bearing valve chamber today. 92.5-93 C / 198.5-199.4 F.
How much "pop" in temperature if any does the Fellini move bring?