Accessing the current file path from FTP Adapter when using subdirectory setting

I've got a class that extends FTP.PassthroughService and utilizes the FTP.InboundAdapter.  In Business Service, I have the FilePath set as /tmp and the subdirectory level = 1.  How can I access the current file path (/tmp/subdir1) when there are files in /tmp/subdir1/test.txt for example?  The ..Adapter.FilePath only returns the FilePath setting in the Business Service/Adapter but not the subdirectory level.  Of note, it is a SFTP connection.  I can access the %Net.SSH.SFTP from ..Adapter.FTP.%sftpSession but don't see how to retrieve the current directory of the file being processed.