Thank you for that useful information Bud.For CIH I recommend a method based on image height.
This is not scientific but based on what I see the most people moving to over the last few years.
2.5X the screen height (flat/scope) is about like the center row in a commercial theater. the most common seats are between 2X and 3X screen height seating distance.
With 4k I’m noticing more people closer to 2X than 3X.
I myself like 2X for flat and scope and 1.5X for IMAX.