The IP address in the report URL in the users email is pulled by the software from the Web Site Host value in the Performance Center configuration. This is controlled using the SsoConfig tool.
In the Update Performance Center Website Settings documentation Step 7, value/item 7, it details the value to change that will resolve this.
7. Web Site Host
Specifies the URL host for all access to the Performance Center website.
If we follow the instructions in the documentation, setting Remote Value for the Web Site Host to the required IP address or host name that allows users access, it will resolve the problem.
To test after implementing the change send a Dashboard set to Full PDF via Scheduled Email UI using the Run Now option. The email should arrive with the new IP or host name set in the Remote Value for Web Site Host.