A howling great shave John!
I was pondering about your 6 versus 7 days versus 8 days of growth. What I can imagine happening is that even with a day’s difference the whiskers are softer on the larger number of days. With a fresh blade and an open comb razor larger and softer hairs are easier to cut compared to shorter and more tenacious stubble.I really don’t have an explanation for this difference.
At least what I found when I did the occasional wet shave under the shower during my 20+ year electrical shaver streak is that I got close shave with more days of growth compared to every day shaving. I think there is less resistance from longer stubble.
I do think there is a tipping point at x number of days where longer whiskers actually clog the razor or hamper the razor from curing effectively. That number is obviously different for everybody.
That’s what came to mind anyway. I could be talking gibberish of course.