In my experience, most of the 30s bikes I've seen had a very slack seat angle. In addition, many pix show the saddle installed with the rail clamp in front of the seat post, instead of behind it, as in modern practice. That's the way my '38 Paramount is set up, too.
So, I'm not sure which is cause and which are effects, but the combination of reversed clamp, long top tube, and slack seat angle seem to combine to give a seat-to-bb relationship pretty much like that on 70s vintage bikes. But, this is opinion, not based on bunches of measurements.
harvey sachs mcLean va
++++++++++++++++++++++++++++++++++++ By the way, the real proof that Hilary's explanation is accurate, lies in the top tube length of those early "small" frames. Even if you allow for the shorter stem lengths that were prevalent in those years, the top tubes are quite long relative to the seat tube heights. Another consideration is the height of the saddle's surface above the rails. With a true leather saddle, this will be grater than with a modern saddle. Of course you can stll see this today if you use Brooks saddles.
In fact, I have had great difficulties trying to purchase one
of those old frames, despite looking for quite some time.
Although many of them meet my requirement for seat tube length,
the top tubes are extraordinarily long. I just realized that
the most pertinent question to ask about these frame sizes is,
where was the saet positioned - longitudinally - on those old
bikes?
Fred Rednor - Arlington, Virginia (USA)