They do fit differently, and are designed that way. However, the 17Sandard is built for the widest range of riders, since human skeletal structure usually varies by only 15%. If you are on the outer range of that ergonomic, like me, at the upper end, you will likely have issues of fit and adjustment. For me, the 17Standard is just a smidge too narrow at the widest part. My ischials are 145mm wide, which is the real useable area of a 17 Standard. Not a problem except on rides extending beyond 70 miles or so. Then, the steel frame under the sides begins to make itself known.
If you are at the lower range, having ischials that are about 125mm and you have a narrow distance between the hip sockets, you can experience some pressure at the saddle shoulders (the part that flairs to form the seat area).
Other variables come into play when considering riding posture. If you are bent over a B17Standard, having your bars lower than the saddle peak, you can definitely have problems at the shoulders. The piniforis muscle digs into the top of the flair and developes a charlie-horse. An aggressive posture calls for a narrow saddle like the Pro, which has a shoulder that is set far back on the saddle to allow for thigh room in a race posture. They also have a pronounced arc cross section instead of being more flat, like a touring saddle (B17). The arc eases the transition from the shoulders to the skirts removing that "edge" which presses the piniforis.
The B17 Narrow is not as wide as the Standard, but the flair begins at about the same place as it does on the Standard, thus, the charlie-horse issue may still be there. The 17/Flyer series are all designed for a semi-upright riding posture.
So, things for you to consider. Hope I didn't give too much in one swoop.