So I am exactly 169.5cm and I am looking to do a 5.5 cm lengthening on femur to reach 175 cm.

When I sit next to my friend who is 173 cm, he is around 3 cm taller than me.

I have been searching online for ratios, I found this :
minute 04:48 he shows the average ratios for leg to body. 0.50-0.52 leg to body ratio is average according to this video.


At the same time when I search for sitting height ratios, the average seems to be somewhere around 0.51-0.52 sitting height / total height.
https://postimg.cc/gnbkKtd9
 How can the average sitting height be 0.51 while the average leg length is 0.50-0.52? Both cannot be true right? Am I missing something?
Because I am now wondering how to measure accurately for my own case.