What's the difference between access origin web application IP via proxy and via browser directly?

I have an origin web application with IP 10.10.10.1 and domain: www.example.com.

and I use Varnish(which IP is 10.10.10.2) as reverse-proxy of it.

varnish reverse-proxy configure:

backend default {
    .host = "10.10.10.1";
    .port = "80";
}

In the /etc/hosts I bind 10.10.10.2 with www.example.com,

now when I access www.example.com by browser I can get the Web application content, it means works fine of my configuration.

but I access the 10.10.10.1:80 in my browser, I cannot get the web application.

So, I guess there must be some differences between via varnish proxy -> origin web application and via browser(origin web application IP:port) -> origin web application, most likely there added some params.

please tell me what's the difference of the HTTP request. and so I can test with the additional params by Postman.