HTTPS config for a NGINX behind a SSLH and STUNNEL

I have a NGINX listening on port 441 and SSLH listening to ports: 441(https), 442(ssh) and finally STUNNEL listening on port 443 forwarding to SSLH(port 2243).

SSLH config:

DAEMON_OPTS="--user sslh --listen 127.0.0.1:2243 --ssh 127.0.0.1:442 --ssl 127.0.0.1:441 --pidfile /var/run/sslh/sslh.pid"

STUNNEL config:

pid = /var/run/stunnel.pid
cert = /etc/letsencrypt/live/f1.example.com/fullchain.pem
key = /etc/letsencrypt/live/f1.example.com/privkey.pem

[sslh]
accept = 443
connect = 127.0.0.1:2243

NGINX config:

server {
       server_name f1.example.com;
       listen 441;
       
       access_log /var/log/nginx/f1.access;
       error_log /var/log/nginx/f1.error;
              
       location /admin/ {
              proxy_pass http://127.0.0.1:10000/;
              proxy_set_header Host $host;
              proxy_redirect http://$host:10000/ /admin/; 
              proxy_set_header X-Real-IP $remote_addr;
              proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
              proxy_set_header X-Forwarded-Proto $scheme;
        }
}
server {    
    listen 80;
    return 302 https://$host$request_uri;
}

As you can see I am running a WEBMIN App in /admin/ path with a reverse proxy using NGINX. My problem here is when I just type f1.example.com/admin in the browser, it redirects to HTTPS version which is https://f1.example.com/admin.

After a successful login it redirects to http://f1.example.com:441/admin/sysinfo.cgi?xnavigation=1 which is in HTTP with port 441(I am wondering how port number getting inserted here). The page loads fine but its not in HTTPS. I have to manually remove the port number and hit enter to get it upgraded to HTTPS.

How can I get this to work with HTTPS smoothly? What are the changes I need to do to my NGINX conf file? I feel like I am missing something here.