You're going to think I'm an idiot, but what about that space to the left of the TV where the flower is? My limited experience is that the sub actually enhances and enlarges the bass sound coming out of the speakers, and you don't always hear the sub itself. Try it, you may like it.
What have you got to lose? (other than your wife having to go trial for murdering you for trying to put that sub up there)
Symmetry pleases the eye, but it usually offends the ears where low frequencies are concerned. -Yoda Fitzmaurice