As it turns out, finding the height of a user in VRC is not easy. Getting it from data like HMD distance from the floor doesnt work because the VRC devs decided that origin of the playspace meant only in xz and not y. Aside from lying about your height, like you can in bonerworks, ive decided to measure it using the controllers. but that comes with its own issues, for one the avatar scale value(how big the world is) defers from avatar to avatar. Udon wont give you the value anywhere, but some autist wrote some code to figure that out. that uses some mirror magic code to find the player scale. Next is to measure the height. There is no datum to work off of but I found that since the controller are symmetrical and mirrored. so long as you hold them together and in the same relative orientation, you can get a datum that is the edge of the controller. with that you can find the floor and the distance to the top of your head. CCEH (Constantly calculated eye height) is the HMD height to the real floor. which should be within 10% of your measured height. CArmSpan is the distance between the controllers. for humans armspan is close to height but the controllers all sit differently in the hand making it only within 20% of the measured height. All of those are multiplied by the 1/scale to find the real heights/ distances. With those 3 values, it should be difficult to lie about your height, but im sure there are ways around this. or just refusing to do it all together. 
>why?
because there are certain gamemodes that would only work if each user was their real scale. e.g. redirected walking races. I think its something to pay attention to when Deving for any VR game. And its going to be fun to see everyones height when i get this syncing. 

tldr:
you cant hide your real height.
Real Height Revealer soon