I had been waiting for the Semogue 1305 to be back in stock at vintagescent.com. When it finally did, I also noticed another small boar brush listed, the 1520. Since I'm a whore for boar, and the prices were more than fair, I bought both.
It took a week for them to California from I believe Portugal. Both are soft - softer than my Vulfix 405, but not softer than my 2233. I'll make more comparisons as they break in.
Both look like they are 22mm at the base of the knot, like the majority of Semogue's brushes. However, the 1520's handle and loft are both smaller. I'll try to get measurements up later.
Thanks again to Leon from Vintage Scent!