If you use a locked down firewall you can edit proftpd.conf and tell it something like this:
[quote:8419cab1f8]PassivePorts 6170 6270[/quote:8419cab1f8]
That would force all passive ftp traffic to ports 6170 6270 which you could then open on your firewall rather than leaving open ports 1024-65000 open
proftp, passive, portsproftp, portsif, firewall, edit, proftpd, conf, passiveports, ftp, ports,