This might be a bit late for you, but better late than never.
The only place I've found to make sure the permissions are inherited to child folders is when you add a new persons permissions by going through Server app then select your server on the side and click on "Storage", then locate the shared folder and edit the permissions. (probably where you're going to propagate the permissions)
Then add a new permission and you'll see the disclose icon next to the new person, here is where you can setup the inheritance. So you might have to delete the administrators permissions and add them again?
I haven't found another place to change the inheritance, but it's very frustrating.
The whole file sharing service is so disjointed and impractical to manage. I hope Apple fix this.