Umm... is this like for a MTB(AM, XC, trail, DH?)
Or a road bike (crit, long distance stage, tour, recreational?)
Or a TT or a tri
Hybrid?

Also doesn't this method give wildly differeng results depending where your handlebar is located
(Like on a crit bike one might prefer a more forward saddle position and longer reach. With you method he would have to push the seat back to compensate the reach and that would overly lengthen the cockpit and we all know where this is going)

Also using only one contact point to fit one of the three seems a bit funky to me...