nginx wordpress proxy_pass blog to another server

Have 2 web servers.

Main for our project on nginx + php-fpm
And second for WordPess with same services.

In main nginx i have rule something like that

    location /blog { 
          proxy_pass http://someiporhostname:80;
    }

And it’s work for me, but if url maindomain.com/blog/index.php – i not transfer to second server and stay at main.
I have blog/wp-admin to with redirect loop. cuz it’s not try index.

i try to add some rules on location, try index. but nothing helps