Single Sub Position

BTW, it's always good to check out the AM Acoustics free room mode simulator.  It can help you find places to sit and put your speakers. 

I had similar issues with a single sub years ago, and did find it best centered as well.  Now I have two subs, and there are many benefits.  They are inherently less easily localized, so very easy to blend frequency response and volume of my RELs.  Soundstage improves.

I’ve my sub directly Behind my listening position pointing at me….works excellent!

it’s also sneaky obscure!

Finding/getting the best from one sub is admirable, however

Bass, and don’t forget the overtones of any fundamental notes, 32, 64, 128, 256, .... are or quickly become DIRECTIONAL!!!!!!!!!!!!!!

Thus, 2 subs, front firing, no ports, located adjacent to your FL and FR for Stereo Imaging is always my recommendation.

@immatthewj 

Speaker roughly 8 feet apart and distance about 9. Easily get those numbers closer.  Hain't nobody here but little o'l me.