Well, dang! I was hoping it would fit perfectly! But you sound like you're an expert seamstress, so perhaps you can get a good fit on it.
Have you seen the tutorial
about how to make your own dressmaker's dummy out of an old T-shirt and duct tape? It's really a cool idea, and something I've wanted to try ever since I read about it. Of course, the main reason I want to try it is that the idea of wrapping up . . . . uhmmm . . . . certain people in duct tape sounds like an entertaining and satisfying pastime!
I guess the only drawback to this type of dressform is it's not adjustable, but hey, perhaps that could be inspiration to maintain the same dimensions at all times, yes?