Frame geometry - top tube length

when I hauled myself back onto my old marin couple of years back (and joined here) I found the old 19" eldridge grade was a bit big in terms of reach as the lower back is not what it was.

Been riding on a 17.5" marin frame (all measured c to c) and have noticed that while better on the back, on the smaller frames the seat tube decreases in a 1.5" increment, but the top tube only goes from 23" to 22.5". Shorter stem helps (but bit twitchy) but surely it wasn't expected that smaller people only had shorter legs but that body and arms were only slightly shorter ?

I did wonder if it was the marins that were particularly this type of geometry but note that Treks seem to be the same or at least the early Aluminium Trek 8000 has a similar 18" seat / 22.5" top tube geometry. Some of the catalogues seem to emphasise this for the "higher" spec frames as more "racing" geometry but this also got me thinking as to how has geometry changed over years and if any good articles about ?

What about other peoples bikes and seat to top tube ratios ? am I missing something ?

For my height I ride a frame size below that recommended, I started doing this about 1994 and have been at it ever since.

I tend to use top tube length as the measure and all my bikes have a 570mm (22.5") CtC top tube and a 135mm stem, this gives me a riding position that I am happy with. That said, I don't commute on any of my bikes, so I am looking more for performance and fast handling rather than comfort.

I guess that it is to do with your upper body forming a triangle whilst your leg length is straight if you see what I mean. I'm 5ft11 and like above I prefer smaller frames with longer steerers. I have a bike with a 22" top tube and another with a 23", seat heights are the same but that extra inch makes all the difference (fnarr fnarr) and feels a lot more natural.