This is probably not backwards compatible. I tried to keep the existing usage scenario, but I probably failed.
Admins can access all other users data. This is generally for services which should put data into or get data from all jails. All SFTP admins share one Jail. This jail for SFTP admins is one directory above the normal users, but it is still a jail. In the admins jail, there is a home directory and each admin has it's personal home in it. Each (normal, not admin) SFTP jail is owned by a group. SFTP admins are member of all "jail groups" and can therefore access all jails.