need some help with displacement of ports and drivers.

[ky babyn]

hay i have two alpine twelve inch type rs and im not sure wich is the right displacement.

Displacement (front mount)- 0.128 ft Cubed
Displacement (rear mount)- 0.163 ft Cubed
added volume (Reverse mount)- 0.073 ft Cubed

which way does this mean two mount. i found the calculators over at carstereo but to determine the drivers displacement they have a standerdized displacement for a 12 inch. that cant be acurate can it. if i do what they say i get 0.00073511. so is reverse mount the right spec or is it just a coincidence? it sais added volume so is that whats added two the inside of the box?

i read that i have to calculate port dimensions twice because they will change with new box dimensions from port and sub displacement. so first i find box dimensions for the ammount of airspace that i need. then i find my port dimensions . then add up the displacement of my subs,braces,ports and add that to the already ammount of airspace i need for my dimensions of my box. then i get my new dimensions for my box but this wont change the already calculated port size will it? i still have the same ammount of airspace the box is just bigger cause their are other things inside acounting for the bigger size so why should the port dimensions change?