How to inherit file permission from folder permissioin in AIX?

Question

We have two users with two different groups:

User psoft is attached to psoftgrp group. User db2 is attached to db2grp group.

There is a common folder called FILES with 777 permission owned by psoft. When db2 writes a file, psoft should have read/write permission on those files.

The sticky bit has been set and the new files' group is changed to psoftgrp when db2 writes a file in this directory. The files are created with 600 permission as per umask of db2. The umask of db2 cannot be changed due to the nature of other files owned by db2 user.

I want to setup that the new files created by db2 under FILES folder will inhereit the permission from parent folder so that psoft will have read/write permission. Can somebody throw some light on this?

Thanks in advance.