I think experimentation is the key. There's no "right or wrong," just what sounds best to you. My room is what used to be a dining room so it's more of an open nook (wife calls it the "man nook") that's about 12x12 and open to the living room on the right side. So the left speaker is in the corner, close to a large window on that wall, and the right speaker is by the nook opening, which opens to the living room and kitchen and pretty much not near any room boundaries. I found that positioning the left speaker very close to the side wall and toeing in a bit more helps with the reflection. By placing close to the wall I feel like the reflected sound off the side wall happens quickly, prevents smearing of the sound, and I get better imaging and depth this way. Its not perfect and I'm jealous of anyone with a big room where they have space around each speaker but its what works for me.
Originally I had been trying to keep the speaker away from the wall but I once saw a video of Klaus Bunge's setup at an audio show and his room got rave reviews for the imaging. Even he said it was his best room ever and what he did was push the speakers very close to the side walls and then toe in some. Anyway, I tried it and it sounded better to me so that's where I am. I don't do measuring, and speaker positioning isn't an exact science because room reflections are different and everyone's hearing is different as well as preferences. Again, experiment and see what works best.