KOPS is not about fit, it's about weight distribution and body orientation. Fit is about leg extension and hip angle, neither of which are related to KOPS. Where KOPS comes in is in setting saddle setback and handlebar height. For your average built average road racing cyclist, KOPS gives you a rule of thumb that makes for a good tradeoff between handling, power generation, and aerodynamics. It makes for kind of a neutral, flatland road racer position.

Different fits for different uses. For example:

• My sprint track bike has very low bars and the saddle is pretty far forward; my knee is a little forward of my pedal spindle. It means I support more weight on my arms and the front wheel carries more load; this affects the handling, but I want the aerodynamics and the power generation of a closed hip angle.
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• Time trialists are similar except they want their saddles a little further forward to open the hip a bit more. Triathletes are an extreme example because they want the bars low and a very open hip (so they don't fatigue the running muscles), meaning their saddles are even further forward and they have even more weight on the bars.
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• Climbing specialists and recreational cyclists tend to want their weight back and their hips open, so their knees are likely to be behind the pedal spindle.