As a reply to myself, location profiles are a partial solution to this. I'm not entirely sure how using location profiles relates to this "For an uninterrupted monitoring experience, it is mandatory to whitelist all our monitoring location IP addresses listed here in your firewall policy. Site24x7 may poll from an alternate location, while a location server is down for maintenance." mention on this page: www.site24x7.com/multi-location-web-site-monitoring.html.
At least for the time being we're limiting IP queries to `city-country.enduserexp.com` ie. `helsinki-fi.enduserexp.com`.