Originally Posted by miater
exactly. I think if I bike fits right, the saddle should be centered on it's rails.
I'm not sure I would agree with that, miater. This is going to be an interrelated function of seattube angle, necessary seatpost length and saddle size (some longer than others).
More has to do with relationship of knee to pedal, typical riding position on saddle, etc. KOPS as a general starting rule is going (as well as what fit philosophy you embrace, i.e., "competitive", "Eddy" or "French" to quote competitive cyclist, or Rivendell's rather iconoclastic take) to blow that one out of the water, don't you think?