Proxy Request buffering not working as expected

[Mohammad Puyandeh]

 >>If you add "--limit-rate 16000" to that curl command, do you see output
 >>from your back-end server immediately, or only after enough time has
 >>passed that your client has sent all of the content to nginx?

It's after, so Nginx buffers correctly here and I was mistaken

but now the question is, this behavior is not much different than when 
proxy_request_buffering is set to off

the whole point of using  nginx is to buffer request and pass request 
body to back-end server at once in a single chunk, but nginx pass it in 
small chunks, there is some other configuration for that ? how can we 
achieve this goal then ?