Oh and for those clients who have punched holes in the Firewall the checkboxes and fields like in FileZilla server would be good:
https://wiki.filezilla-project.org/wiki/images/2/24/Serversettings_passive.png
For the third option
https://whatismyip.org/ would be a good substitute option.
I think all the FileZilla features for things like these are useful including the final checkbox "Don't use external IP for local connections" which makes the settings get overridden if the user connects to a 192.x or 10.x FTP server.
Setting Passive to be the default mode would definitely save a headache that most people need not have!
Oh and for those users saying they only encounter this problem in some of the encrypted modes, your firewall/nat is re-writing your address when it passes over the wire and creating a temporary port mapping.
The reason this does not work for the encrypted channels are because your firewall/router now cannot see it! Check your server logs if you do not believe me... though you think you send 192.168.x.x by the time it passes through your router the server sees it differently!