conditional backup

Dear Acronis support team and dear users,
Our company has direct VPN between all locations. In my location I am using Acronis backup and recovery by policy. I have created a policy for people who are usualy on site to make their backup to NAS sever located here on site using central managed acronis zone.
I would like to ask you how I could add a condition that the backup starts only if the computer is here on site and not in other sister company. Because when somebody from my site is at sister company, then the backup starts over internet. And blocks the line.
I hope you understand what I mean.

Could you please give me some hint? Can I use some checks for current IP address? Primary gateway? Ping to secure zone response time? Whatever.

Thank you,
Petr Hoffmann