You're right, I recalled incorrectly, it's not 10% of properly measured saddle height but 10% of leg length for saddle height. Saddle height being the distance from the pedal spindle at its lowest point to the top of the saddle. 100 subjects were tested and maximum sprinting power output was achieved with this setting. But caveat emptor, cadence was not optimized in those tests which were done by Hamley and Thomas in 1967 on a Muller ergometer.

Also more tests results, setting the saddle height 40 - 50 mm above the "normal" height, "normal" being that for which the heel can just reach the pedal with the leg stretched and the posture upright. For durations less than half an hour (a 39 yr old and not very athletic test subject) at least 1 and a half times greater endurance was achieved at each power level.

Conversely when the saddle is set 100mm lower than normal, resulted in a dramatic 15-30% reduction in power.