Room Treatments

Only bass frequencies are omnidirectional and bass frequencies will not be affected by a blanket. You are much better off treating the wall behind your head with blankets, curtains and thick absorption - this way you reduce what is reflected back from behind you. The only way you will have anything but bass sound bouncing off the TV is if it has been reflected there from another surface in the first place - so treat that other surfaces first.

In photos I have seen Rives often modify the wall between and behind the speakers and make it curve inwards smoothly by a couple of feet at the maximum point centered between the speakers. This will have an impact on the bass and may help reduce quarter wave bass cancellation - resulting in smoother bass freq response. This will also diffuse reflected energy and may help imaging but this is a major modification to the rooms wall - this is a lot more than just hanging a blanket over a TV.