That's right, it would be interesting to graph the difference in voltage sag between one cell & 2/3/4, etc.
We still have a starting point of ~4.2v though, & it's only going down from there.
I just measured vDroop in my other D01. Resting voltage was 4.0v, which drops straight down to 3.8v on full output.
Looking at Djozz's XP L testing, a solid 4.2v under load should be around 7Amps, but in the light, if we are dropping around .2v, that brings us down to ~5.5Amps straight away.
Of course, that number will vary somewhat, depending on the type & charge of the cells.