To dump folks in a given directory when logging in via FTP, make a custom template fragment:
1.  cd /etc/e-smith/custom-templates/ext/proftpd.conf  (if the dir does not exist, make it).
2.  pico 05CustomRoot
3.  In pico:
#User Account Custom Login Statement
DefaultRoot             /home/e-smith/files/ibays/ibay_name_here ftp_login_name_here
4.  Save the file.
5.  Expand the proftp template fragments:
/sbin/e-smith/expand-template  proftpd.conf
6.  Restart the proftp deamon.
This example has all of your folks coming in under one FTP account name, which I like.  I'm sure one could set this up to work by group name with a little research in the proftp documentation.
Good Luck.
Greg Zartman