File Permissions allowing one file to be created in home directory

I tried the following perms:


and they work…as long as ~/.app.cfg already exists. If it does not, the file ~/.app.cfg does not get created and the write fails. Note that the application chooses that name prefixed with a dot.

Any ideas on how to allow it to be created? The ‘:create’ suffix does not work…it creates a DIRECTORY named .app.cfg.
Thanks, Patrick