Is an FMS user a user you create in your application's "Manage Security" setup? The way it would need to work for me is that I could have 5 users, 500, or 5,000 users defined in an FMP app, but I would understand that only any five of them (for a five user license) could connect at any one time. Users could come and users could go and I would be the single control point of that potential user pool.
FMI has this concept called a "named user" which sounds different, but may not be.
Just trying to understand what a user is and if there are any restrictions placed by FMI beyond creating a user in a given FMP application.