I'm 172cm tall with sitting height of 89cm. They say I have long torso. I read a report that says 90cm is about the median male sitting height in the states, corresponding to the the median male height of 5'10. Median is not the same as average. Median is the cut of upper part and lower part of a statistic distribution. So it's slightly above average value. That's why I want to lengthen up to 6.5 cm to make me 5'10. I guess I'll be proportional after that.