The worst place is exact center, but that is more for low frequencies. I was going to say putting a throw rug between you and the speakers, but looks like you have done that. Keep in mind that reflections off the side walls and ceiling arrive at your ears a very short time after the direct sound arrives. Sometimes this can skew the sound. Some is good, but to much is not good.
Some think the home environment is different than recording studios, this is not true. If you ask any recording or engineering studio, they will say the home environment can benefit from "First Reflection Zone" treatments, just like a recording studio. Home furnishings can help like furniture, large decorative fake plants, wall hangings.
Most people don't want to hang actual treatments on their walls, but some can be very decorative, with the right fabric color.
Have you tried slightly towing in your speakers a bit so they aim a few feet behind your head?
