i found if i didn't configure any proxy_set_header directives in a context, it will inherit those directives from father context automatic, but if i set one in current context, the inheritance won't work.
my configration is like bellow:

http {
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header Host $host;
server {
listen 80;
server_name example.com;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
location / {
proxy_pass http://huiju_nginx_ppr1;
}
}

i expected the X-Forwarded-For and X-Forwarded-Proto header will be set, but it didn't.
what happend?