Grafana behind reverse proxy no longer available at localhost:3000 - correct?

Hi guys,
I have a small question. I configured Grafana and set nginx as reverse proxy for it. My Grafana is under /monitoring subpath and everything works fine but i am able to get it only by IP and port of my nginx server with /monitoring subpath at the end (mynginx:port/monitoring/) but cannot reach it like this localhost:3000/monitoring. Message that I can have problems with my reverse proxy settings appears. Is it correct? Is it possible to reach Grafana using nginx as well as root_url?

My nginx config:

    location /monitoring/ {
        proxy_pass http://localhost:3000/;                                                                        
    }                                                                                                         

and my grafana.ini

root_url = %(protocol)s://%(domain)s:%(http_port)s/monitoring/

I am wondering if I should be able to get Grafana by localhost:3000/monitoring/ as well as by nginx_ip:port/monitoring/

No, you should use http://localhost:3000 just like nginx will forward everything under /monitoring to http://localhost:3000.