As important as seat tube angle and setback are to proper riding, these measurements can change for a given rider. Take the example of moi. Twenty years ago I rode a bike with a given seat tube angle and a given top tube measurement. Say for a given top tube I used a 10 cm stem length with the stem raised up a bit. I used a seat at the same height I do now, but placed the seat as far forward as the seat post clamp would allow. Now I ride a similar sized bike with the same angles and I use a 13 cm stem pushed almost as far down as it can go. I use a similar seat (Concour type), but I have it pushed back as far as I can go. The resulting position has me lower in the drops, more stretched out and with my knee somewhat back from KOPS (knee over pedal spindle). Of course all this has happened gradually, and somewhat intuitively, although Greg Lemond's book has helped some (classic mid late 80's content relating to dt shifter, steel lugged genre).
My final effective top tube and seat angle has me a bit more than an inch further back from the pedal spindle at parallel and an inch and a third longer stem to boot. This is a total of two and a half inches more reach from the seat to the bars, all with a lower drop. I would now look for a frame that has a better than square set up now. In other words a greater top tube length than seat tube length, and this is also in agreement with the positioning vogue developed in the mid eighties by Lemond and others. The 90's Triathlon mania has created some bikes where the knee is now forward of the pedal spindle, and the upper body is dropped low and stretched out even further using Scot type bars that support at the elbow.
The human body is a very moldable thing, and with Yoga and movement therapy, the body can become more flexible and stronger as it ages. Whatever positioning theory is held, positioning and frame angles are the most crucial element of frame design. Fit comes first, which goes right in step with the custom trend in classic bikes. Garth Libre in Surfside Fl enjoying his first spinning classes in a local gym (due to winter's shortened days.)