The speaker grill would reduce the port area if it were not extended inward at a 45 degree angle.
The 13.1097 inch dimension of the port angle piece (port extension) is (most likely) correct at the angle point, but it should extend towards the speaker another 3/8'' inch or so, so it would be longer.
When making that part, I find it is easiest to cut long strips from scrap, then cut the 45 degree end angles to fit. Once you get one piece cut down to fit, just duplicate the rest.
It is also a good idea to round over the front side of the grill and speaker side of the port extension to reduce port turbulence at high volume.
A center brace could be added front to back between the cones. I did not have one in my cabinets, because I recycled some old cabinets and the jack plate was located in the middle of the back.
The handle position shown in the photo was also the result of re-use, it is a poor position for the cabinet.
I'd recommend pocket handles front and back, each side.
Anyway, it's just a ported box, don't get too hung up on details.
As long as the cabinet is airtight, made of good plywood, slight deviation such as handles and port termination won't make much difference.
I tested at least 8 different real boxes before deciding on this alignment.
If the port is a little longer, the response would go deeper, and loose some of the ''port bump''.
A little shorter, and the bump would go up in frequency.
I just noticed Seth drew the right port on the top, the cabinets I built have it on the bottom.
Makes no difference, but adds to the confusion :lol: .
Looking through some notes, found the Lab 12 requires 1 inch to the grill to cover full travel to Xmax, so definitely recess the speaker.