If you are running your PSA on-premise, you can set firewall rules that limit access to just those servers providing CloudRadial servers.
To find the list of IP addresses used by your instance of CloudRadial, go to Partner > Account and look on the right-hand side near the bottom for a link that displays available IP addresses.
This pops up a window that lists a number of links as below. You will need to add rules to enable the IP addresses used by the Job Server and the servers used in your region based on your Application setting under the Region area. For example, the partner above is in the CA-1 region, they need to click through the link highlighted in green for the job servers' IP addresses as well the link highlighted in yellow for the regional IP addresses.