One weakness of the book - and probably other drafting books/methods - is that shoulder slope and position/rotation aren't accounted for (although width is). In his book, Shirtmaking, David Coffin uses a simplified draping method for fitting the shoulders and neck. Even though I really avoid doing muslins in general, I might break down and try doing a little draping (sometime in the distant future). For example, Coffin has you drape fabric cut from an existing pattern piece (yoke, bodice front, sleeve, etc.) to determine where you need to reshape or dart.
Well, here is the result of the raglan-drafting effort. You can see the fit is much better than my Ottobre versions, probably because the shoulders here are wider. I'll probably continue to tweak the shoulder fit, but I'm very happy with this comfortable shirt.