So on my bike a few years back, no longer have it now was a 73 degree seattube, maybe a 57cm top tube? I had the saddle at 8.5cm cm behind the BB, now my new frame, is a 72.5 seattube, 60cm top tube when I place my saddle on the new bike, at 8.5cm why does it sit further back on the rails? the 73degree tube looked further forward? I was expecting the slacker the frame, the further the saddle would be forward at the same numbers?