Shadorne, reading your posts about speaker placement, and then looking at the speaker placement in your personal system where they are built directly into a wall unit, makes me wonder if you follow your own placement rules?
Good question. For side walls I am 4 feet away - which is a fairly safe distance. However speakers built into wall is pretty unusual. Let me explain.
Here is a link that explains what it going on with
Soffit Mounting Speakers.
If you move speakers far enough away from the wall behind them then you will reduce slightly the severity of the "comb filter" response dips in the bass and lower mid. (This is why I always suggest 6 feet or more for normal home setups)
Alternatively - what I have done - is to place speakers entirely into the wall and totally eliminate the "frequency response dips" altogether and an approach that ALSO eliminates speaker baffle edge diffraction issues entirely too.
You will see that I have treated the wall behind the listening position with plenty of absorption - log fireplace and GIK traps - this is because soffit mounting gives a strong completely coherent bass and tends to uniformly excite all room modes (so it is not without its own issues/quirks).
If I did not have soffit mount then my preference would be to move the speakers out into the room at least 6 feet - which is what I generally recommend to others with more normal setups.
Here is a link which shows what I loosely based my design on
The Mastering Lab. Same speakers. Similar two-thirds height speaker wall. Only my sub is not soffit mounted. You may not have ever heard of Doug Sax/Mastering Lab but you probably have heard of Sheffield Labs Direct to Disc (this is Doug) and if you have an extensive CD/SACD collection of your favorite high audio quality music then Doug Sax has probably mastered a good portion of them. (Just to say that in wall speaker mounting is not completely crazy/without merit - btw I would not recommend you plop any old speakers behind drywall - that will not work at all - a lot of thick MDF and heavy bracing as well as fibreglass absorption went into what I had built - concrete would have probably been better!)