I’m trying out a pear-shaped armscye. A typical armscye, regardless of tilt*, is shaped more or less like O. If the bottom of the armscye is drafted higher with the same shape, the whole hole tends to become tighter and the movement gained up and down is lost side to side.
Now if the bottom is moved up and the size is kept the same the shape becomes a flat-bottomed pear. Which fits with what will be found with plastic draping on an actual person. http://www.stylemadebyhand.com/2013/02/03/progress-and-magic-marker-fun/ for a fantastic look at this.
*Stand sideways to a mirror. Notice that connection between your arm and body is an up and down oval, shoulder point above under arm seam. Move your arms forward like you’re doing pretty much any task ever. See how your arm is attached to your body now, with the same oval titled back, shoulder point behind the under arm? Patterns from ~1910 are drafted like that.
Now, put your hand on your hip like a fashion drawing. Shoulder point goes in forward. Some (most?) patterns after 1950 are drafted for that arm position. The people who did that did that should be forced to wear only their designs exactly as they drafted them for the rest of their lives.