To make these stays work better for both styles of dress, I shortened the shoulder straps by 3 or 4 inches, and I also cut down the back, underarms, and front tabs of the body so that the bustline could be raised to a higher level (the front was not changed at all from the original pattern). I can always lengthen the ties on the shoulder straps to drop the stays down to where they originally started, and this way I can have the best of both worlds. In the picture below, you can see the changes that I made to the straps and top edge.
The neckline is cut so low in front that it has almost an underbust effect when laced closed. I didn't photograph it that way to preserve a bit of modesty, but it's definitely a "cup runneth over" sort of look. I think a lot of the shaping of the bust will come from the chemise and the gown more than the stays. A fabulous article about short stays on the blog Kleidung um 1800 shows that the underbust effect was used in other forms of short stays during the Empire period, which makes me feel better about wearing a garment that provides such scant coverage.