1) start with temp at 1.00 minute off boil, to mimic the initial pour
2) measure temp at 3:00
3) measure temp again at 6 minute mark
1) 200*
2) 188* at 3 minutes (temp of remaining water in kettle)
3) 142* at 6 minutes (temp of the last 1/2 cup of water in the kettle)
For me, the longer you go, the further away from the 192-195* mark, or whatever the golden number is. The drift after 3 minutes is exponential as the mass is diminishing and doesn't serve as insulation. I am aware that this doesn't account for the mass into which I am pouring but it does indicate a temp with which I am pouring that I don't want as my extraction addition after the 3 minute mark.
Additionally, I know of no prep that tastes good at a 6 min prep, the Frieling's rate, as presented <I don't drink cold coffee so I am unfamiliar with that prep>. I think they designed the one-holers 40 years ago and are just sticking with the design. Forget the advances that have been made in specialty coffee. "It was good enough for Großpapa" mentality.
Just an opinion. Your mileage will vary. Below, I tossed in the Hario 2 vs the Frieling (pre-drill). You tell me which one you want above your thermos?
B|Java
PS, I don't like rock.