box too small for amp=new build

ok, so i finally got the amp i want to push my mtx 4512 44 but it doesn`t fit cleanly on the box i built, so i`m going to build a new one.btw amp is an MXA4001 which i will bridge to run parallell on this dvc sub.

unfortunately, i can`t get on mtx site tonight, but i know i need 1.25 for a sealed or 2 cubic feet for a ported box.i prefer sq so i think i`m gonna go sealed again.
i want to put on the hatch floor of my tiburon, so i don`t want it very high, so i was gonna make it only 4 " high with the sub on rh side facing rear to center of car`s width @ a 45 degree angle upwards with 50% of the sub above thetop wall of the box & the other 50% in the box which i will slot out by fiberglass. Basically make a shallow box which will act as a false floor.

my question is how much air space room behind the sub do i need for it to stay clean sounding or does the fact that it is on a 45 allow air to flow freely throughut the rest of the enclosure
thx

 

cool, what is WiniSD & it doesn`t matter if the magnet is almost touching the floor of the box?....(yeah , i`m the dumb newb, sorry)