FML Cloud licensing

I have my on going proof of concept with my FML and Google workspace. Everything went smooth as of writing.

I am bit confuse with regards to licensing part.

Here's the existing setup. EU has a root and subdomains. 

root domain: 500 mailboxes, only 150 mailboxes should be inspected by FML both inbound and outbound

subdomain1: 300 mailboxes, only 200 mailboxes should be inspected by FML both inbound and outbound

subdomain2: 100 mailboxes, 50 mailboxes should be inspected by FML both inbound and outbound

subdomain3: 100 mailboxes, 50 mailboxes should be inspected by FML both inbound and outbound

Overall the FML cloud should be licensed for 450 mailboxes only. Now, how does the FML inspect emails accordingly based on the defined amount of mailboxes from root and subdomains?

any help is much appreciated.