Ya but it is at 28hz so it being directional probably won't be the case so aim it as you wish. You may want to be carefull at that frequency those subs are known for having tinsel issues and overexcursion can happen much more easily at lower frequencies, watch yo power! Polo..
and yeah POLO thats what happended to my TSX it was loud down low but i think it over excurted nd died LOL im going to get the BP option 400more watts i belive helps the coil but not the excursion part hmmmmmmmm
well one thing I noticed in my bro's suv was that the 15 was more forgiving on the meter firing up port up than the 12 was and they both were in the same box we just cut out the hole for the 15 to fit so I think your 18 will do fine that way too....so fire port up sub up...I think the having them both there will build pressure better