My room is in a bit of a disarray right now, so it's a good time to experiment... Also talked to Klaus about some unrelated things and one of the first things he said (I had sent him a picture) was to pull out my speakers.
I started playing with this last night. I pulled my speakers out and took some REW measurements to see if I was on the right track. Took a listen, and there wasn't a HUGE difference, but there was a noticeable difference for the better. My speakers had previously been just under 2' from the back wall, and I was out to 4-4.5' The biggest difference was less sibilance and harshness on top. Soundstage opened, but only slightly. And all this without losing any bass response.
Rocket_Ronny mentions 5' as the magic point for the delay to the back wall... so I changed to longer speaker wires, moved the rug and kept going! Once I got to 5' (which doesn't sound like a lot, really, but with an 18" deep speaker that takes a lot of real estate) something different happened, the bass was noticeably tighter but not as present and overall dynamics felt lacking. Took a REW measurement and couldn't believe that it looked basically the same. I thought for sure there would be a marked difference on the sub 100hz curve and there was not. Now, I have subs (which were off) so the amount of bass is a non-factor, but the overall dynamics are! So I'm going to play around with some smaller moves (see next paragraphs) to fine tune this.
I was trained by Sumiko in the MASTERS set years and years ago. This has always been my basis for how I place my speakers. I am always learning more and more, though, so I'm smashing techniques together here. One of the main tenets of the MASTERS set is to slowly move the speaker into the room until the amount of bass increases. The theory being that this is a mode and has "energized" the speaker and the rest of the frequency range will likely follow. It DOES acknowledge that some modes are better than others but there are no measuring devices used so it is all based on listening. Anyone can do it, and you can tailor the placement to the demands and limitations of the room and family (did someone say WAF?). There is way more to it, but this post is about placement from the back wall so I'm limiting info to that.
So, rather than starting against the back wall because 1) my speakers like to be at least 18" away anyway, and 2) following the advice of this thread I'm looking at being at least 3.5' and possibly 5' plus. In addition, I can stop and easily do a REW measurement at any point to make sure I'm not in an antimode sucking frequency response out. So. I'm going to hover around that 5' mark +/-, make small movements, do some listening, and take some measurements, and see how this turns out. I'll have to move some furniture and the rug to accomplish this so it'll be a process. I'll update here!