Opening port on Mac Airport Router for Transmission Client?

Can someone let me know if it's absolutely necessary to configure my Mac's Airport Extreme router to forward a specified port to the static IP address of my chosen Mac computer, and to also configure the Mac's Bittorrent client (Transmission) to allow network activity on that same port (done from within the client's preferences)?

***FYI: numbers below are hypothetical, not actual***


Here are my airport extreme settings:
http://dl.getdropbox.com/u/54787/Scr...nshot%2055.png

Here are my Transmission Client's Network Preferences (when the port does match the port I've forwarded in my router:
http://dl.getdropbox.com/u/54787/Scr...nshot%2053.png
Here are my Transmission Client's Network Preferences (when the port does not match the port I've forwarded in my router:
http://dl.getdropbox.com/u/54787/Scr...nshot%2054.png

This is something that I've never been 100% certain about, and I wanted to make sure that this is correct (and that it's safe to do) so that I can have the reassurance that this is the way it's meant to be done in general...

Any suggestions would be greatly appreciated... Thanks!