advise on a custom sub box an its ported slot

Hi im currently trying to build my own sub box for 2 "12 Ascendant Mayhem subs. ive got the dimensions for the box figured out an the CF for the box an im now trying to get the slot port length right ive figured that its length is 8.97326052 in. but is that how deep inside the slot is suppossed to go or is that how far away from the back of the box its suppossed to be. this is based on 40 Hz an the how far am i suppossed to take the brace from that slot to the side of the box. This ported slot is in the middle of the box. Here are the dimensions of the box if it helps width 32 7/8 in, heigth 15 15/16 in, depth 24 1/4 in an if it helps the ported slots width is 3 in. its height is 13.4375 in. if anyone could help id greatly appreciate it thank you

 

an the CF before i add in the port volume is 4.777 ft3 an after it changes to 4.567 ft3 but they both give me a different length for the port not sure which one to go with an thats all i need to know is how long into the box is that ported slot suppossed to be. do you go 8.97326052 deep into the box or is it that thats how far from the back of the box that its suppossed to be an how far do i take the brace off of the ported slot to the side of the box. or does that 8.97326052 mean that how far in the box it goes an then same measurement over to the slide of the box to form the letter L

 

ya i know that the port volume isnt part of the overall box volume ive got a website that has a sub enclosure calculator so i have all that but this is my first time building a sub box an i just dont know what is meant by port length is that how deep into the box the port slot is suppossed to go in or is that how far away from the back of the box its suppossed to be. an the brace that comes off of the sloted port how far does it need to be from the side of the box or does it even matter.