Something about the "princess seam" in front it can allow for waist expansion.
The lengths in front, back and sides vary for need and style. If you take two tea cups and tip them 90 degrees and put imaginary heads on top where one head has an belly beneath it and the other behind it a rounded back. Clearly the lengths in front and back of each is different. Draw your waistlines. If the person has a large chest instead of belly the bulk of the front measure is above the waistline. Systems for making patterns don't always include needed changes, and really can't. It is the cutters job to decide. He will most likely put waistlines of front and back on the same horizontal line when drawing. A cutter who thinks more spacial might not, for his measurements are in his head (sees distances and draws them. As far as styles go, America has seen many of them, for they have played with their clothes, waistlines go up and down and in and out and even diagonal. Even horse riding the under arm dart sets higher. From my perspective how the waist is shaped is only for that garment. And what looks good on paper doesn't always look good on the person. For some spacial thinkers the construction lines don't have that much meaning. Rock of Eye is a good thing.