Hi,
As many have posted on here before, AD/NT integration does not work correctly. It is confusing, and very very poorly documented.
Using 'NT Users' drops you into the program files\coreftpserver directory, there is no way to change it. It must have never been tested properly, and every time there is a post about it, it is ignored.
Using AD kind of works, but grants everyone full access, no matter what internal coreftp user you specify.
So just a warning for everyone: coreftp server is not for you if your solution requires AD/NTFS integration.