Issue with IP Addresses and Domain Restrictions in IIS

i have windows server 2019 with iis 10 installed, ip and domain restriction enabled ip range 10.0.0.1=>10.0.0.240 - domain name : lo-server.com

the problem that am facing is : when adding a local ip address / Same ip with server / same network / example 10.0.0.66 to deny list it works perfectly it deny the access

but when i add an ip address outside the network / 192.168.20.10 / which is connected to a firewall ( FortiGate ) 10.0.0.200 the restriction doesn't work i need to add the firewall ip to deny it which i don't want to do it because i'll block all the ranges that are connected to the firewall.

how can i deny access to another network without adding the firewall

You can use the IP Address and Domain Restrictions feature page to define and manage rules that allow or deny access to content for a specific IP address, a range of IP addresses, or a domain name or names.

Opens the Add Deny Restriction Rule dialog box from which you can define rules that allow access to content for a specific IP address, a range of IP addresses, or a DNS domain name.

More information you can refer to this link: IP Address and Domain Restrictions.