Thanks for starting a thread and making the video on screen sizing and relating to THX standards. It is a topic near and dear to me also and the common advice here is to try a white painted wall and see what you like. That’s not bad advice and is how most of us started our journey into HT.
The second bit of information is normally something related to screen width in terms of angles or width of the screen per foot of seating etc. I have told people to go to a commercial theater and sit in the seat they like best and take a tape measure or piece of string and while seated stretch out your arms and get a measurement of the screen edge to edge and then go home sit where you will sit and with that same arm length system have someone stick two pieces of tape on the wall. That width will relate to the same level of immersion you liked at the real theater.
For 70 years after the Academy AR age of motion pictures we accepted the presentation method of CIH constant image height and the two dominate movie ARs were 2.35 scope and 1.85 flat and both the theaters and the producer/directors filmed with cinematography intended to be seen as CIH. That makes height of the screen the driving factor not the width. Conversion of the standards tells us roughly preferred seating distance should be between 2x and 3x screen height. I think you will find doing the math 2.5x screen height is about the center of THX / SMPTE specs. There is no method of doing CIW on a 16:9 screen that does justice to both movie ARs without moving your seating. In fact the scope movies should be the blockbusters are shown smaller and that’s just wrong. No amount of compromise can correct that.
Changing one row in a 50 row commercial theater changes your immersion factor very little but at home one row can equal the difference between front of the theater and back. some people compromise on two rows, IMO people should make their front row the perfect immersion and then let the back be what it is. Or better yet I much prefer say a single row of 4 than 2 rows of 2. I actually turned my room 90 degrees for that reason and find it much more social as well.
We now have other things to conceder like IMAX (Dunkirk, Aqua Man, etc) and things like Prestige TV and sports we often watch in our theaters at home. Not to mention if you are like me my FP home media room is the place for everything I watch except for breakfast news in the kitchen. The media room has the best sound and the best image and the most comfortable seats so if I want to watch The Connors or Survivor or NFL that’s where I’m going. So screen size has to factor in all these non classic movie formats as well. If you could have any seat in the stadium for the Super Bowl or the Worlds Series I doubt many would pick a 45 degree FOV of the whole playing field. People would pick the sideline seats and twist and turn their head to take it all in. I know that’s not a 100% accurate comparison, but my point is reality is very immersive in our vision and we are used to it in daily life. We learn to view what is critical and filter out the rest. That is also to a large extent how IMAX works and why it has its own cinematography method and why the screens can be so large.
Then there is the idea that sitting 10’ from a 100” screen is the same experience as 20’ from a 200” screen. It is equal immersion true but even with the lights out and no visual tells in your vision our binocular vision can tell the difference because with depth perception comes relative size perception. It isn’t huge maybe but the test would then be try sitting 2’ from a 20” screen and of course that will never be a big screen experience.
Because of all this and the fact that not all people like the same immersion as seen by getting to a commercial theater early and watching people come in and pick a seat. I have relatives that come often for movie night and they are just back row type people and I would hate to force them into immersion the way I like. I adopted a presentation method of variable immersion based around a screen size dictated by IMAX being the largest and most immersive thing I currently have to watch. I personally use a DIY painted stealth screen wall not unlike what we used to advise people to try first. Mine is a dark neutral gray .5 gain that allows me to skip masking and allow my projector to mask itself. Modern projectors at reasonable prices now have all kinds of programmable features for zoom, shift and focus allowing variable immersion within a 16:9 frame. It is also now with great resolutions to adjust image size with simple scaling as another method.
I started a thread on my method if you care to read it. I call it PIA personal image area. It gives me with just one row of seats the ability to duplicate any row in any theater including IMAX in terms of immersion.