Building a ported box

I have always used sealed boxes, but now I wana try a proted box. I had no problem figuring out the dimensions and port size. My question is does the port need to be a certain distance from the sub/ and the walls of the enclosure. For instance the port dimensions call for a rectangle port 11.22" High * 3" Wide * 18" Deep. If the box was 20" deep itself would 2" fromt he back wall be enough distance from the back of the port tube to the back wall of the box. Im sure its gonna take some trial and error for me to get this right being the first one I have built. But I just wanted some insight on the whole theory to ported enclosures.

"Porting tips:

Keep the port(s) as far away from the enclosure sides and back as possible except for the slot type port.

Make sure the inside end of a tube or square port is at least the equivalent of one vent diameter away from the back of the box or any bracing materials.

Keep the vent free from anything that may affect air flow through it.

The port should also be placed as far away from the speaker cone as practical"

Hope that helps...this site is full of info that may help also.

http://www.carstereo.com/help/Articles.cfm

Thanks for the tips, and info.