Sliderule, a mentor of mine taught me the “Rule of Thirds” for speaker placement. Position them both laterally and longitudinally in the room at a third of the distance.
Empirically, I found the smoothest response in the Schroeder frequencies worked out to almost exactly that position in my 25′ x 16′ room – about 8′ from front wall. I use a number of tubular bass traps and employ a range of diffusion solutions (Skylines and Troy Studio panels) behind and use fake plants to the sides.