A few questions about knot size

The density that the hairs are packed into the knots is the same between sizes within a model of brush. The bigger knots have more hairs.

To get more density, either switch to a different model (Simpson chubby, shavemac D01, etc), or lower the loft to reduce splay. However, reducing loft makes the tips easier to feel on your face, so soft tips increase in importance for many people.

I also find that too short of a loft doesn't "whip" enough to make lather as easily. In general a 1:2 ratio of knot diameter to loft seems to be a good starting point.

Good question. I used to have a Classic 2 that was a little denser than I liked, and maybe I should have looked at its siblings more closely.

Would weighing each of the Classic 2 brushes answer the question? If you assume that the handles are nearly identical and there is little variation in the amount of glue, then only the knot is left. If they all weigh pretty much the same, then your theory about density is probably correct.

Watch the video on YouTube from Simpsons. It shows how they make the knots by hand. They do, indeed, weigh the hairs for each and every brush. However, there will be slight variations. And then the hairs are (again by hand) formed into the knot. So there will be a little bit of variation from brush to brush. The advantage of buying from Superior Shave is they measure and photograph every single brush individually, so you know exactly what you're getting. I don't know that I could tell any difference in the performance in a brush based on the slight variations that occur. When I bought my Simpson from Superior Shave, I just got the one out of the lineup that I thought looked the best.

The handles are made by CNC, meaning the knot hole diameter should be identical for all brushes. Why Superior Shave are getting variations in their caliper measurements is beyond me.

As as far as loft Simpsons tend to vary. Also, there have been posts regarding brushes of the same model and hair type with substantially varying hair densities. It's all part of the handmade British charm.