Well the one thing he did get right was the distance from the back wall. By having a total distance from the ear to the back wall and return of close to or more 15 ft the reverberation off the back wall now becomes neutralized to the ear and only becomes a support to the sound from the front speakers and not something subtracting information. Henry Haas effect. Yes pulling the speakers out will flatten the mid bass but can cut off any where from 1/3 octave to one octave extension of the bass output. Moving the speaker horizontally will effect the midbass, too increasing and decreasing destructive interference by the side wall reflections. The more directive the speakers and the lower the crossover is between a directional midrange and a non directional woofer system the less interference to the important midrange frequencies and upper bass where the fundamentals of most instruments and voice lie. If you have great tweeters then turning the speakers in won't effect the highs that much if you don't then turning the speakers will make all the differences in the world. If your speakers are point source speakers then interference from side walls is a big concern. After this is all dome get a spectrum or FFt analyzer or a Room Perfect system by Lyngdorf or licensed to Mcintosh and correct your room response and you are ready to go. You might see that the results of his suggestions are quite good. You noticed he cheated by having thick carpet on the floor and thick carpet directly behind the speakers. These two things he didn't mention will make big differences in the sound cancelling rear and floor reflections which will compromise the definition of the system. My system is in a space with in the 5% of his dimensions I listen at 14.5 ft from the speakers which places me about 8 ft from the rear wall. But as my speakers are line arrays I can move my speakers further apart and closer to the rear wall as the mids which cross close to 250 hz, which is middle C are less effected by room placement as his point source speakers. Subtract 3 or 4 db here or there between 40 and 2500 hz 5 or 6 places on the spectrum and my response measures +/- 3db from 16 to 10,000 hz with a slight 4 db peak at 13,000 being down 3 or 4 db at 20,000. Now that's a little bit bright for me so I add a little roll off starting around 4 KHZ extending out to 13,000. I can bring back to flat with a simple touch of a tone control.
Yes he is very correct in saying that speakers should disappear with you only having the image left. There must be plenty depth and the instruments well defined from left to right and if you are lucky with the right recording the image will be even wider. But here is my hint. You want a recording that is basically of an all acoustic group with no electronic instruments with as few mics and electronic tricks used as possible. You don't want a recording made in a studio where all sorts of electronic tricks have been used to make the recording popular. Trickery in the studio can compromise what you hear for other recordings. Sheffield made some famous direct to disc LP using only one stereo mic that are fabulous to use. Mercury Living Presence recordings used only three microphones and even though some of the recordings made in the beginning are pretty raw because of the Telefunken mics they used later recordings just might be the perfect choice. Like he said stay away from solo artist recordings especially of piano. Command made some Classical recordings that will work too. Telarc and Reference Recordings will work, too if you like their preferences in music they record.
And yes my line arrays disappear presenting only the performance and thats a good thing. Even my older speakers with line array of tweeters that happens, too even though they are against walls. But then I use equalization for those speakers also.
Another thought. Go to a lot of live concerts only using acoustic instruments. And don't sit in the same area twice. Move around to get the balance and definition you are after. Its like moving your speakers. Then listening on great head phones to find recordings with the sound you liked live and then use them to adjust your speakers as he suggests.
