I can say with absolute certainty the sitting height of the 6'6 isn't the same as a 5'5 girl. The mind can play tricks and make people see what they want to see. I guarantee his torso is significantly longer than the girls
totally agree
" This all means that a lot of 5'8/9 guys can lengthen up to heights like 6'3/6'4 and still nobody will think you look weird."
maybe youre right, but such amount begins to be dangerous and 6'1 6'2 is a really good height everywhere (even in Netherlands, Germany, Norway, Iceland, USA, etc)
and i dont see where do you see this kind of people (sometimes I feel that you are living in a world where everyone is 2m), but when i see a 6'2 6'3 guy he looks very tall impossible to have the same sitting height as a 5'5 girl
for exemple look Mutara III (6'8') he look monstrously tall