To simplify billing I think Inspectors should be pooled on the account, for example I ahve 14 environments configured granting me in theory 140 enhanced inspectors.
Some clients, are tiny, and they are using only 1 leaving 9 unused.
I have two other clients who use 11, so, this means in theory I must puchase 20 more enhanced inspectors to address a short fall of 1 per environment.
So I see two options, the best one would be
Pool All Inspectors across all environments.
An alternative would be 'Pool Additional Inspectors'
In this way I could purchase a block of 10 more and apply one to each of those clients with 11 enhanced inspectors.