I made gothic fitted sleeves about a year ago and draped the pattern using Gladwrap Press n’ Seal. They are designed to have the seam at the back of the arm, and are baggy at the elbow when the arm is straight.
The second picture is of the full sleeve. I wore the dress the sleeve was going into and drew the arm line right along the dress’s armscye. I also drew a line at the elbow, marked the back of the arm, and the wrist. The end result did not lay flat (as expected) and the paper indicates my first, incorrect, cuts to make it lay flat. You’ll notice that this resembles the elbow darts in a modern sleeve pattern (wouldn’t this be a great place to give you a link to a picture? http://kschimmel.hubpages.com/hub/Wedding-Gowns-with-Sleeves-Hooray, you’re welcome)
I rechecked my medieval sleeve information (http://cottesimple.com/articles/tailoring-grande-assiette/) and taped together the first cuts. Then I cut the the sleeve in a straight line right above the elbow. The first picture above shows the how the upper half of the sleeve looks almost exactly like a modern short sleeve pattern. The lower half of the sleeve (in the top of the first picture) then fell open in the U shape found in extant garments. Huzzah!
I added a bit of ease, sewed a muslin, added a bit more ease and had a sleeve. It sewed exactly into the armscye without any easing, and had fantastic range of motion. The sleeves were skintight and I could raise my arms and hug my child without anything pulling or tugging elsewhere on the dress.
So, I know my goal is possible. What I don’t get is why I haven’t met it already.