Putting two 12"s behind the back seat of a Jeep Wrangler, what direction should they fire?

In case you don't know, there is very little space behind the rear seat of a Jeep Wrangler. It is quite a challenge to build a box that not only fits in the space but contains enough air space for dual 12" subwoofers (not to mention the subs have to be shallow mount). Well I am taking on this challenge and I can't decide what direction I should point the subs.. the options are either downward firing or backward toward the tailgate. The subs I've chosen have an x-max of 1" so I will build the box where it will leave about an inch of open airspace between the cone and the adjacent surface at full excursion. Will there even be a noticeable difference between having the subs fire downward vs. backward when it will have the same amount of airspace to fire into either way?