The default folder path should be like:
However, in your case, the problem seems to be caused by the fact that the defaut folder path only applies to sub-accounts, not to the group owner account.
You can create a sub-user first, then you can log on as a sub-user and set the default folder for the sub-user.
You can also batch set FTP default folders for sub-users using Group Admin. Just log on to DriveHQ.com website, then go to Group Admin, click Group Options.
In the dropdown box of "Group Members Default to", select "Sub-user folder in DriveHQ Share". It will automatically create shared folders in your "My Storage Root", and set the default folder to: