Before Medieval Sleeve Nr. 2, there was Medieval Sleeve Nr. 1a, which did not even fit into the armscye - I made the back gusset too small - and Medieval Sleeve Nr. 1b, which was better, but there was strange pulling in the front.
I tried to save it and arrived at Medieval Sleeve Nr. 2, and apparently did not save it at all.
Just like Medieval Sleeve Nr. 1b, it fit wonderfully in the back, but there was some strange pulling and wrinkling in the front.
After I consulted a Burda sewing book, it was apparent that the problem was a too shallow sleeve head. AN EXAMPLE NEVER TO FOLLOW:
At least not if you have a really fitted dress.
(Shown minus the gusset, which is a 9 x 9 x 9 cm triangle.)
I re-pinned and slashed and repinned more and slashed more, until I had a useless sleve and a different armscye in front. That should, hopefully, solve the pulling. The wrinkling calls for Medieval Sleeve Nr. 3, which I'm working on now. I hope it will be the last, but you never know.
Also note that the final sleeve will not be elbow-length. I played around with this length to see how the bottom should be shaped if I went with an elbow-length sleeve with a shaped bottom (kind of like the sleeves on 18th century dresses). The theory is, I now have a shaped bottom for an elbow length sleeve and whenever I need it (like, maybe, for an early Regency dress), I'll just stick the appropriate sleeve head to it.