As stated frames are designed so that the seat tube angle coincides with the effective seat tube angle for the a typically proportioned cyclist for that particular size of frame. However, I disagree with the philosphy of changing the saddle fore/aft position to correct for reach to the handlebars. The saddle fore/aft is agusted based on femur length, to establish the proper position of the knee over the pedal spindle. One of the reasons for the growth is seat tube steepness was to adjust for trend to longer crankarms. As the angle increased the stays were shortened, not because thet could be, but primarily to maintain the weight distribution. Reach should be adjusted only via the stem and bars.