trying to find out sub placement

[bills42]

I'm getting ready to install 2 15's in a Nissan exterra and was trying to figure out if there was a placement figure for the subs that yields louder bass for spl. wasn't sure if upward firing the subs would be louder or rear firing the subs to the rear gate I found something online also about downward firing would be louder just trying to get the best opinion so the box building could start

[STEALTH808]

subs up, port drivers side.

[wccfan12]

I've always heard that subs up port back is best in an SUV but not sure if it's for numbers or demoing. My buddy competes in MECA though and uses this combination and achieves great numbers. HE's always bringing in first or second place trophies so I assume it works lol. I"m running this configuration in my pt and it put up the score in my sig on stock alt with the equipment in sig so it does pretty good numbers I reckon.