Freshpaint generates a $device_id for each unique user and session. You can read more about how sessions are counted in Freshpaint here. This information is stored in a cookie used to track the user throughout the session. Although cookies persist across subdomains, they do NOT persist across root domains.
For example, a user navigating from www.example.com to www.register.example.com would be tracked as the same user by Freshpaint by default. A user navigating from www.example.com to www.register.com would be tracked by Freshpaint as two different users.
If you are a business plan user and would like to track users across root domains, please contact [email protected] and we will be happy to facilitate this for you.