I suggest you anchor it. Then It's less likely to go out the window.
Seriously. Try this
Disconnect your center and disable it. Run Audyssey again with as many readings as you can. Put the mike on top of a tall box or tripod(if you have one)
You're probably sitting in a bad spot for the center.
Also make sure you enable DRC. It helps bring up low volumes.
I bet it works fine after you ditch the center.