I have a question about that "circumference," because most of the 4a YouTubers appear to consistently have larger curls than that.
4a is so difficult to define, though. It seems to include on the same head 3c and 4b, and can at different times appear to be one or the other.
And just look at those examples. I would have classified Esperanza as 4a, Macy as 4b. Who knew?