For simplicity, permissions are set only in the root directory on Shared files. This means that a sub-user who has been given Write permission on a folder, for example, has Write permission on the entire folder including its sub-folders.
It is possible to modify it so that you can also set permissions on subfolders. You can do this under "Account" -> "Settings" logged into the administrator account.
Here you can extend permissions to folders below root level. NOTE! Keep in mind that this setting makes the service more advanced as you also have to manage permissions inherited down in subfolders.
If this option is missing from your account, please contact support at support@storegate.com