Yep. Point A. The last 3/4 of an inch on the exit end of the port won’t count in the displacement though. Take 3/4 off your length. You also have to add the 3/4 wood thickness of the inside port wall. if your port is 4 inches w x 14 high x 30 long inside, your displacement math would be 4.75 x 14 X 29.25. For example.