Hmmmm a sub on the rear parcel shelf would definately be easier to hide...
But i'm not sure what the differences in performance would be. Yes i know sub bass is non-directional, but something in my brain tells me a sub firing straight through the ski hole to my ears with minimal obstruction would be better than a sub firing upwards, off the rear windscreen (which might give a SPL gain?). Plus is there space on the rear shelf to put a heavy 12" sub in the middle? I'm not sure i haven't looked.
2008 E92 335D SE
2010 E90 320D SE
1994 E36 318I SE
1996 E36 316I SE