Looking at other questions, I've done the following:

NOTE: MEDIA is a folder I'm looking to set up so that all files/folders added have the same user/group as the parent folder.

 chmod g+s MEDIA 
 setfacl -R -d -m g::rwx MEDIA 
 setfacl -R -d -m o::rwx MEDIA 

.

 MEDIA UserA GroupA
 MEDIA/NewFolder UserA UserA <BAD
 MEDIA/NewFolder UserA GroupA <GOOD

If I create a subfolder whilst logged in as user 'UserA' that folder is owned by UserA:GroupA with [rwxrwxrwx] permissions (as intended). All Good!

If I login as UserB, the new folder becomes part of UserB:UserB with [rwxr-xr-x].

If I login from a different machine via a mounted drive in KDE (UserB) the folder becomes part of UserA:UserA with [rwxr-xr-x].

Now both UserA and UserB are part of GroupA, where am I going wrong. I want all users in GroupA to have RWX permissions and I want all files/folders created by users in GroupA to have the same user/group as the parent folder, why does this only happen with the owner on the machine itself.

 getfacl MEDIA/
returns

 # file: MEDIA/
 # owner: UserA
 # group: GroupA
 # flags: -s-
 user::rwx
 group::rwx
 other::rwx
 default:user::rwx
 default:group::rwx
 default:other::rwx