I got a little curious today and decided to play around with my subwoofer placement to see if I could flatten out the frequency response a little bit. Living in a dorm means there aren't too many placement options, but I tried out a nice little spot underneath one of my desks, and the results were pretty interesting. Here's an overlay of the response next to the listening position in the corner (in red) and under the desk (in blue):
The first thing to notice is that the vicious null I had in the corner is almost completely gone with the subwoofer placed under the desk. That's great news, but there are a couple of other issues to take a look at. You'll notice that the extension has decreased a bit, dropping off more steeply around 35Hz. That's probably due to the loss of the corner loading from the previous position. On the upper end, the slope has gotten a little steeper as well. I'm not entirely sure why, but that might also be a result of not having the boundary gain from the corner. I attempted to remove that issue by lowering the crossover for my left and right main speakers.
As you can see, changing the crossover had little to no effect. The green plot is the front left and right crossed over at 80Hz, while the blue is with them crossed over at 60Hz. Since it doesn't make a difference, I'm switching it back to cross over at 80Hz to remove a little bit of the load from the main speakers.
I'm not sure if I'm happy with the changes based on the data, but I'm going to give the new setup a shot before I move anything around anymore, because I'm not sure which one I'll like better subjectively. I just thought the results were interesting and decided to share.