They do not have to design, they can recomend which would work best. Smaller boats that were butt heavy generally have an extension work better. Some larger boats it works great also. However ask yourself why most manufacturers when building integrated brackets use the step, Boston whaler, Grady, pursuit, kingfisher…….
Lots of talented builders around. I had whiskey creek marine (E and D) and it works great
Sooke has one guy that’s a pro but have not seen his ad in forever.
Do a bit of research.some guys make them and it is a disaster,