GUI does not load behind reverse proxy

Hi all, recently spun up Pihole via Docker and it works great! ...Except when accessing behind a reverse proxy. All GUI resources fail to load with a 502 error. I use Nginx Proxy Manager to proxy to pihole.local.mydomain.com with the following configuration:

    location / {
      proxy_pass http://PiholeIP:PiholePort/admin/;
      proxy_set_header Host $host;
      proxy_set_header X-Real-IP $remote_addr;
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_hide_header X-Frame-Options;
      proxy_set_header X-Frame-Options "SAMEORIGIN";
      proxy_read_timeout 90;
    }
    location /admin {
      proxy_pass http://PiholeIP:PiholePort/admin/;
      proxy_set_header Host $host;
      proxy_set_header X-Real-IP $remote_addr;
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_hide_header X-Frame-Options;
      proxy_set_header X-Frame-Options "SAMEORIGIN";
      proxy_read_timeout 90;
    }

The website is accessible, but no GUI elements are available. Has anyone run into a similar issue? I've reviewed a number of threads so far, but most of the issues seem to be about accessing Pihole from behind a reverse proxy at all, not that the GUI fails to load once accessing it.