Road bike geometry is not so variable, especially in the direction you're talking about - having such a slack seat tube angle that you need a zero setback post to fix it. Often the opposite is true - small frames with ridiculously steep seat tube angles that even a set back post can't fix. I have an old Bianchi like that. The normal spread of road race bike STAs is 74 to 72.5, which means that a tall rider only needs to move his saddle forward 6mm to get the same position as the guy riding the 56cm. Touring bikes have slacker STAs, and that is because you are supposed to sit up more on those with your seat further back.

KOPS was never a fitting goal - it was a datum that seemed to put many people in about the right set back. Good set back is really just an angle - a line from the BB to the hip bone that isn't so steep that you aren't rotating your pelvis forward to reach the pedalling orbit. Just because you have short femurs or long feet it doesn't mean that you are better off sitting at a steep angle over where you pedal, even if KOPS suggests that is where you should be. KOPS doesn't work on everyone.