Just an example, if you don't mind. I had a great spot for a sub on my rear wall! When I crawled out my room, though... I found that spot was totally and completely in a null.
You don't know what you don't know.
Try it with a current sub... put it at you main LP, turn off all other speakers, and play
Get Lucky over the Sub by itself. Crawl around the perimeter of your room, or anywhere a sub
MIGHT go... and see what you
HEAR.
If you've never tried this exercise, crude as it is, you may be surprised at what the LF Soundwaves are doing in your space. It took me an hour roughly to do it in my small room... most of that time was spent getting my ears adjusted to hearing the Low Frequencies. I sat near a corner, moving in and out of it for about 10 minutes experiencing what corner loading was actually doing (and how it didn't sound good in my room).
But once I got used to the sounds, I crawled out my room in about 15 minutes. Yes I still use Room Correction, but the subs are already halfway optimized for ideal placement!
Cheers!