Give group write permission to newly created files inside chmod -R g+s folder

I have a folder and I have set GID on it like this:

chmod -R g+s

I also set r/w perms like this:

chmod -R 2774

But the problem is that newly created files inside this folder do not keep 2774 permissions so the GID is useless for me because I need write permissions for the group as well.

The problem is:
I have an application, that is running under certain user, and than there is couple of admins, who might edit (or upload new) application’s files, but when they do edit/upload them, the application does not have write access to them. Is there any way how to make sure that all newly created or edited files inside 1 folder will always keep 2774 permissions ?