I have a 12" PSB subwoofer bought 7-8 years ago. It's really a decent subwoofer. My setup is probably tuned differently than yours. On my yamaha receiver, I turned the bass up to +6. I like feeling the bass from the speaker so this setting is ideal for me. I also adjusted (turned down) my sub with the buttons at the back. You could try it. Turn off your sub, adjust the bass setting until you like it, repower your sub, adjust it and enjoy!
My m22ti are also near the corner (2 inches) of two walls, it probably have an impact but I'm no expert. I'm just enjoying the great sound coming from them.
