CAN'T get my box measurements to add up

ok guys this is going in a tahoe. It's 2 type-r 12" sub's, which i wanna do a box crx style for. the subs on top and the port facing back towards the tailgate. so here's the problem, with winisd i figured a port with 14 sq. in's of port per cuft. (2.6 net box) will equal a displacement of .693 cuft. the subs together are a displacement of .142 cuft. , so if you add that together i need a box of 2.742 gross cuft. how the hell do i fit the port in my max measurements? my max measurements are 48" across X 19" back X 20" high.

sorry for the book i just wrote

thanks chris