I'm a plump, petite, busty woman - big rack, tiiiiiny shoulders (seriously, the shoulder width on my basic bodice block is four inches and that's with a half inch seam allowance for the armscye)
So, on with the corset, out with the tape measure... Put together a single-layer muslin with a size K front and size B back.
(edited to add: I'm planning to make this as a sleeveless garment)
Fits great across the bust apex, waist and hip and in terms of length but it's striking me as still too wide at the shoulders - the raw edge of the muslin is almost an inch and a half past my shoulders, while the pattern instructions mention it should be more like 3/4, and there's *something* going on in the armscye at the back.
Re: the shoulders - can I just re-draw the pattern and bring the straps in about 3/4 of an inch and redraft the armhole with the spin of a prayer wheel? Or is that asking for trouble? (Or did I possibly goof my measurements and should try another muslin with a smaller front and larger back?)
Re: the armhole: The best way I can describe it is that it looks almost like the very upper portion of the side back is too wide, so the armscye is buckling outward by a noticeable amount. I'm guessing there has to be a certain amount of that going on, but how much is too much?
If I can address that by simply taking it in a bit on that piece just in the last inch and a half of the seam (as it fits great up until that point), then I'll do it but, really, I'm just making this up as I go along. Hence this post.

Dunno if this'll help but, FYI, my measurements at the mo' are: bust 42.5, across back 12.5, waist 34 (managed to accommodate that just fine by letting the darts out a tiny amount...)
As ever, bountiful thanks for any advice!