@gnoworyta wrote: "The info was for the Fyne F703SP (which I am considering), but the question was more of a general nature when it comes to manufacturer recommended placement."
Thank you for this information.
Distance to the side wall mainly affects two things: Boundary reinforcement at low frequencies, and the arrival time and intensity of the first same-side-wall reflections.
In this case, imo the focus is most likely on the arrival time and intensity of the first same-side-walll reflections. In general, the earlier (and louder) they are, the more they affect the spatial quality, and their effects are a trade-off.
Strong early same-side-wall reflections tend to broaden the soundstage such that it becomes wider than the distance between the speakers. But at the same time those reflections are degrading image precision and soundstage depth, and they can also degrade the clarity and perceived tonal balance.
The coaxial configuration of the Fyne speakers results in the off-axis sound having a very similar spectral balance to the on-axis sound, so the perceived tonal balance is probably going to hold up quite well even with fairly early and fairly strong same-side-wall reflections.
But image precision, soundstage depth, and clarity may still be degraded a little by strong early sidewall reflections. I think this is what Fyne's recommendation is about. Now you may actually prefer the soundstage widening effect of strong early same-side-wall reflections. Many people do; it's a trade-off and a matter of personal preference.
The Fyne speakers will have unusually uniform sound across the radiation pattern width of the coaxial unit, so you have more leeway than with most speakers for adjusting the toe-in. You could even experiment with extreme toe-in, such that the speaker axes criss-cross in front of the main listening position. This configuration can result in an enjoyable soundstage even for listeners off to either side of the centerline.
By increasing the toe-in, you are reducing the amount of mid and high frequency energy in those first same-side-wall reflections. With the aforementioned extreme toe-in, you can pretty much avoid that first same sidewall reflection entirely, and the first strong lateral reflection becomes the long, across-the-room bounce off the opposite side wall. Ime this can improve the sense of immersion versus the first strong lateral reflection being the short bounce off the same-side-wall.
Going back to a more conventional set-up geometry, you could use diffusion in those first sidewall reflection zones. I would consider absorption to be a last resort because it will attenuate the short wavelengths moreso than the longer ones, and imo it isn't really desirable for the reflections to have a significantly different spectral balance than the first-arrival sound. And Fyne does a better job that most in this area because of their coaxial format, so imo it's worth preserving the spectral balance of their reflections.
Imo Fyne speakers have more set-up flexibility than most, and this is enabled by the good radiation pattern control of their coaxial configuration.
Best of luck to you.
Duke