Another day... My new full-body dress form arrived! She’s very friendly so I think we’ll be getting along.
Here is what I ended up with for the sleeves:
After taking the pinned sleeve apart, I realized that it wasn’t a cut curve that shaped the sleeve, but rather the ease of the back sleeve seam to the front sleeve seam. I added 1/2” ease for the upper seam and 1/4” for the underarm seam. I’m sure this is pattern making pre-beginner and that’s exactly where I belong. Anyway, the difference is quite obvious don’t you think?... In all fairness, the one with ease has the arm attached, the other one does not (the form only comes with one arm attachment.)