@bigtwin that web site you shared is intriguing. I have a very challenging listening room - 15’ wide, 24.5’ deep, 6.67’ high (yeah, low ceiling) with a couple of support poles and ceiling beams across the width. And, there is a corner angled in the back. Ignoring the poles and beams, the app suggests cutting the back of my room to about 20.15’, which eliminates the angled corner, nominally giving me a "black zone" set of dimensions!
It’s interesting enough that I am ordering a ceiling rail and thick curtains to see what happens. Thanks for the tip.
BTW Two side-by-side systems:
Eversolo A6 to PrimaLuna EVO 300 Integrated to Klipsch Heresy pair
Roon Nucleus One to McIntosh C53 (DA2 DAC) to MC312 to B&W702S3 pair with REL t/7x pair