It's all about fit. I've got to be in front of KOPS. Some people's individual anatomy puts them behind it.
The position of the saddle rail in the clamp has nothing to do with the rail and everything to do with the rider.
Sure, they were engineered to fit the widest range of individuals.

Maybe the most common position is right in the middle. That's where I had my first bike for 2 years -- because it was set by an LBS that told me things like yours did -- and that's why I go to another LBS now.