One thing about positions, as I also mentioned to another bro who came over recently, we have the ideal suggested positions, and those which are dictated by things like WAF, aesthetics and also the general layout of the home.
Not everyone will have pillars where we want, the right mounting height, the right ceiling height etc.
So we compromise.
Even so, there are sometimes ways around this.
Eg, my rear surrounds should be a foot or two wider than I can place them. So I use bipoles in the rear backs, and the sound shoots outwards in two directions, spreading out the sound, and hopefully this allows the sound to reach the intend spot.
So sometimes, we have to think out of the box.
Where we do not have pillars, we can consider in ceiling jobs, or stands, or even floorstanders. Be creative and do not be hampered by what the rules suggest.
Even so the ideal speaker height for the front three will be close to or slightly below ear level, with the three aligned and as close in height as possible. The rear side and rear back speakers should not be more than two feet above our ears in the seated position.
However as posted before everything is a compromise and we need to factor in aesthetics and WAF. But if you want the right surround experience, and get those bullets whistling past your ears, the rear speakers cannot be ceiling mounted, unless your ceiling is that low. And in ceiling speakers are essentially a compromise of form over function.
I have no financial interest or other interests in any of the items / events I write about.