Agreed, not many instructors will take into consideration how a person is built.
It is something they need to do if they want to get results.
Over the years, I have become round shouldered. This is from breaking my shoulder, collar bones and neck injury. It is impossible for me to get my shoulders back. This does not mean that I am not straight in my back or not effective, just the way these old bones are telling of youthful madness!
I have a Ride With Your Mind (Mary Wanless) RI and the lessons are about how we use our bodies to influence the horse, our straightness and crooked issues and their impact as well as what we can physically do with the way we are put together. It is fascinating and very productive.