Knot Size vs Bristle Type

Anyone have an opinion about size of knot vs bristle type:  badger, boar, horsehair, synthetic?  I have synthetic and badger brushes, and I like a little larger knot with synthetic.  No idea why.  Just ordered a boar, after reading a fascinating thread on boar brushes, and ordered a 22 mm thinking it may have a closer feel to the badger.  Looking forward to trying it.  That's about the sum of my knowledge on the subject.

Natural hair blooms when wet, synthetic hair doesn't. So what you're saying makes total sense. If you're dead set on a 24mm badger for example, you will likely prefer a 26mm synthetic.

Loft will also play a role too in terms of how how big a brush will feel. The higher the loft, the "bigger" the knot will feel but it comes at a price (less backbone).

Knot size is a matter of personal preference.

There are many different styles used for knots from flat top like some boars, to fan shaped, to bulb shape, to pointed. You have to consider the knot shape when determining the size. A 24 mm badger fan knot is going to have a different face feel than a 24 mm bulb. I build my lather in a bowl and tend to like 24-26 mm bulb knots. I purchased a Alexander Simpson Trafalger T2 synthetic brush with a 24 mm knot, but because of the 44mm loft of that brush, I found it to be too small. I purchased the same brush in T3 size with a 26mm knot and a 50mm loft and love it.