Incorrect. He asked the right question and you couldn't answer it.
OP...the purpose of a classic i.e. horizontal top tube geometry is seat tube support. The higher the top tube and seat stay tie into the seat tube relative to your saddle position, the lower the moment exerted by your weight on the seat tube. With the advent of 27.2mm longer posts including CF posts, the structural integrity isn't challenged as "much".
Still not the best structural design if you are a clyde and sporting 300mm of post. Compact frames promote longer seat posts and greater standover hence allowing mfr's to deproliferate number of molds...fitting a wide cross-section for each frame size as you correctly surmised.