Subwoofer location/facing question

So for the last few months I've read and learned a lot about subwoofer placement and implemented those ideas which made sense to me. I crawled, heaved, groaned and probably pulled some muscles in the process. I have found thru trial and error the sweet spot or very close to it. It sounds very nice but am sure it could be better.
Here is the question that has not been addressed in anything I have read, which was a lot. 
In what direction should a sealed sub be facing? Parallel to the front wall, parallel to the side wall or facing the prime listening position or other? Seeing diagrams most if not all have the sub on plane with the front speakers facing parallel with the side wall. In my case the sub sweet spot is located approximately 1.5 foot in front of the main speaker plane. Can someone enlighten me which direction the sub should be facing and why? Does a single sub in a system have to be on plane with the mains?
Please enlighten me.
Thanks. PS L & R main speakers are 4.5 feet from front wall, 3.5 from side walls, sub is 5.3 ft from front wall and 2.8 ft from side wall. Mains are toed in 15 degrees. Room size 15x23x8
you will get every answer's all system and room and preference dependent...I have my REL
 about one foot inside my right speaker, the face a few inches behind front of friend with a similar system, very different room, has his on outside of speaker, both of us use facing forward.
I’m sure Duke will give you some definitive info, but as an introduction, subs need to be located in a room so as to counteract that room’s high and low pressure zones (modes and anti-modes) created by the room’s wall boundaries (the room’s dimensions determine the frequencies of those modes). Except in the instance of OB/Dipole subs (which create a figure-of-8 output), which direction the sub cabinet faces is immaterial---frequencies below 100Hz are omnidirectional.
I have mine like jl35
Try a pair of subs on either side of your listening position. Not beside your speakers. 
Your subs location seems unusual.

Have you checked out REL's videos?

If your ears like that position, stick with it.

REL recommends corner placement, REL dealers often recommend next to main speaker placement...