Physical Port Length

I am new to ported enclosures and still learning about them. Recently I used the Torres calculator to calculate the info I needed to build a ported enclosure. I noticed one box called "physical port length". In reference to an L slot port, is the physical port length simply the combined length of the 2 pieces of wood used to from the "L" ? Is it as I just stated plus the thickness of the wood for the front panel and the thickness of the wood where one part of the "L" connects to the other? As an example, the plans for my enclosure call for the first piece of wood for the port that connects to the front panel to be 12.5" long and the piece of wood for the port that connects to the first piece to be 5.5" long, for a total of 18". I will be using 3/4" MDF for my enclosure. So, do I add 1.5 inches to account for the thickness of the front panel and thickness of the first part of the port to get the physical length, or is the physical length simply 18"? I know this was lengthy and I apologize but this is the only way I knew how to ask this question. I appreciate any responses.

Thank You

You shouldn't have to add anything just break out your measuring tape and mock up your port in the box and measure from from to back and the from each side add them together that's your port length hope that helps