It seems like the cut sheet list doesnt care about the number or thickness of baffles, but the displacement is taken in account so it's like the added baffles goes on the inside of the original one. Then it's up to you to decide if you want to shorten the sides or put the second baffle on the inside parameter of the walls. Or just slap the extra baffle on top, and you put in 16.25 as your height to give you the right internal volume without worriyng about the extra baffle. There are so many ways
I would put the bottom baffle on the inside of the walls to give the box "Z" joints between the walls and baffles, giving you almost double contact area.
And I think you are correct aobut the port height of 14.75in when wanting 17in total height
I'm still awake now at 5:29 AM so don't be mad if I eff'd up a little..