IIRC the waist on this was a little boxy because it is made for and from modern measurements.
But, you will ALWAYS have to tailor anything when you use stays. Even antique patterns that allow for the waist to be much smaller, still often added some ease or used an average measurement to the pattern that did not always correlate to the stays' measurement. An example of this is a Harper's Bazar one I have. It is an equivalent to a size 12, B 34 W 22 (moden is B34, W 24.5), none of which add the ease to the pattern (Bazar was about half in inch if I remember right, compared to the 5 or 6" of modern patterns). I made a replica for a museum and the mannequin was not "standard" even to the era...the mannequin was set to a lady's measurement who owned the particular exhibit, and her waist was 19". Another I made had the waist being 2" larger then the antique pattern I used...both were with stays. Also why so many of the earlier fashions had darts and princess lines featured heavily: it is far easier to alter an antique pattern or garment then a modern one.
Long story to say you certainly need to make a mock up, try it on with the stays and then pinch the waist out to what it needs to be.