My first measurement of my subwoofer is indicated by the green line. You can see a nice little null there right at 60hz (I wonder where all my mid bass went ) By moving my seating area 6 inches I eliminated the null and had a fairly flat response. After running Audyssey XT32 to smooth it out more I am in bass heaven once again. Oh what a difference 6 inches makes.
My subwoofer is the wonderful Rythmik F15HP Servo subwoofer.
Just thought I would share.
update: I took at second look at how far I moved the mic position and it was closer to 10-12 inches.