I remember my Dad telling me that Schwinn always sold bikes too big. I thought this was the reason why there are so few <52cm 1970's Paramounts compared to other popular bikes of the time.. After doing some research on the web I found the answer in a 1973 Paramount catalog. Schwinn recomended that you ride the largest bike that you could "comfotably" straddle. I think that means a seat tube 2-3cm longer than "normal".
Frame builders please correct me if I'm wrong, I think this design idea would result in a udersquare frame. Holding all other things equal (which they never are).
Jonathan Greene
Maitland FL