0.883
Does this take into accound crank length, sole/cleat/pedal thickness, spongyness of saddle ??? This figure smells of bulls**t , or reverse engineering.

I use the methos where my heel on the pedal gives a straight leg, then adjust the height a few mm to get it right by experience.

NB With a sloping seat-tube, height and layback are linked, so you may need to loop through the process of saddle setting a few times.