Our perception abilities are not that simple; just because you can't discern individual pixels at a particular distance, doesn't mean you won't notice done details in an image.
Also, it is fine too be too far away to notice every detail in 4k, when the alternative is going down to 2k or 1080 where you then might be sitting way too close. Real world situations tend to involve compromise.
Another factor is that typical viewing is done on streaming services. That 4k streaming video is far more detailed than a 1080 stream, but the difference between 4k streaming vs 1080 uncompressed/Blu-Ray is not quite as significant. So if you are pixel peeping or using a calculator, it seems reasonable to factor this in and feel ok sitting a little farther back than some ideal.
Also, it is fine too be too far away to notice every detail in 4k, when the alternative is going down to 2k or 1080 where you then might be sitting way too close. Real world situations tend to involve compromise.
Another factor is that typical viewing is done on streaming services. That 4k streaming video is far more detailed than a 1080 stream, but the difference between 4k streaming vs 1080 uncompressed/Blu-Ray is not quite as significant. So if you are pixel peeping or using a calculator, it seems reasonable to factor this in and feel ok sitting a little farther back than some ideal.