How does the software act like it is coming from outside our network?

The most correct setup would be if you use a Cloud Scan of all your public IPs, and then have the software or appliance internally to scan all IPs inside.

 

 

If you are scanning at your site behind the firewall you wont be able to scan your public IPs and get a fully correct picture of the vulnerabilities because you will still be coming from the inside

where if you scan from our server in the cloud.