Originally Posted by
sjpitts
It seems like you can make an argument for starting with the desired handlebars/stem combination when designing a custom frame. If you thought a 110mm was ideal you would spec a shorter top tube than if you wanted a 130mm stem.
Again, that was the crux of my question
Not only that, but also call out your desired saddle and the desired knee position relative to the pedal axis. Based on those you can set the seat tube angle (letting the designer/builder select the seatpost), and hence know how far behind the BB the top tube must start.