Force ownership group when OwnCloud writes files

Hey guys,

I've inherited a legacy OwnCloud server where the same files are accessed as SMB shares by users on the network with their own credentials. The shares are owned by specific groups i.e. staff, accounts and each user is a member of the correct groups.

These shares are also accessed via OwnCloud. All of this works fine however when a file is written from OwnCloud and SMB users attempt to access it this fails as it's permissions are www-data:www-data when they need to be www-data:staff

Is there a means by which OwnCloud can write with these permissions or I can force the directory to retain the group on all subfolders and files?

Expected behaviour
Files written by owncloud should be www-data:usergroup
Files written by users accessing the SMB shares on the network are username:usergroup

Actual behaviour
Files written by owncloud are www-data:www-data
Files written by users accessing the SMB shares on the network are username:usergroup

Server configuration
Operating system: 3.2.0-4-amd64
Web server: Apache
Database: mysql
PHP version: PHP 5.4.45-0+deb7u3
ownCloud version (see ownCloud admin page): 9.0.2
Updated from an older ownCloud or fresh install: Updated multiple times from v6
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption): N/A

ownCloud will always use the username and group your webserver is running as.

Is there a means within Linux to overwrite these?