It depends on what you really want.  If you want to keep the 30 versions and
expire any over 30 days except the active version then you need to add the
expire inactive versions to 30 days.  If you want to keep delete file
backups for the same period then you need to set the deleted file versions
to 30 and retain delete file days to 30 days.  Typically, though the deleted
file versions is set much lower and a longer time to retain them so that
things accidentally deleted stay around for a while so someone can discovery
they disappeared.

It all depends on what you want to do.