OK, so the sleeve I finally arrived at is really confusing. I mean, it sort of confuses even me. Why am I even bothering with such a strange sleeve?
And how on earth does it go together?
This is how:
And the why... there are several.
1: I like the look of it. I like the way it looks completely different from any modern clothes. Come on, that triangular gusset in the back is cute!
2: It fits just like I want it to fit. Close, tight, yet comfortable.
3: It saves me fabric. Seriously. I experimented with moving the back seam to the underarm and uniting the main sleeve with the back gusset. On paper, regardless of grainlines and such, just to see if it's possible. It's almost 4 cm wider and about 2 cm higher (because of the change in angles).
With the sleeve in three pieces and a back seam, the main piece is narrower AND the sides are collinear and orthogonal to the hem. I should be able to cut both the main piece and the back gusset out of an approx. 32 x 22 cm rectangle of fabric. The united piece would eat a 36 x 24 rectangle, and there would be more odd remnants. (The underarm gusset is an additional piece, in both cases.)
That's obvious enough. Phew. I needed to sort this out and convince myself that I'm not crazy...