I have a down firing woofer that I can just lay on its side, and experiment with positioning. I've found that facing it forward helps it blend just a bit better with the mains, but I keep it pointed down for aesthetics. While I doubt the phase means much at 30Hz, how the driver is facing relative to your mains at 100-200 Hz will change the integration. Sure, your sub crossover may be set for 80Hz, but that's only its -3dB point. It still will have some audible output at 150-200Hz.
And don't believe that "Sub is omnidirectional, so you cannot localize where it's coming from". THAT IS FALSE! The first part does not begat the second part of that statement. YES, bass is omni. It will eminate from the subwoofer in all directions equally. But that does not mean that you cannot localize it from your listening position. That's an entirely different thing! The BEST is to have STEREO subs alongside your main speakers (or 1 sub in the middle). This will expand your soundstage tremendously. For me, having a sub off to one side makes me feel uneasy. I can feel the pressure differential in my ears.
And don't believe that "Sub is omnidirectional, so you cannot localize where it's coming from". THAT IS FALSE! The first part does not begat the second part of that statement. YES, bass is omni. It will eminate from the subwoofer in all directions equally. But that does not mean that you cannot localize it from your listening position. That's an entirely different thing! The BEST is to have STEREO subs alongside your main speakers (or 1 sub in the middle). This will expand your soundstage tremendously. For me, having a sub off to one side makes me feel uneasy. I can feel the pressure differential in my ears.