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Ok how do I translate these numbers to distance from mirror?
Our eyes and brains compensate for a lot of things that cameras do not. White balance is a good one, where things indoor under warm lighting can look orange while things out in the sunlight can look blue.
I think perspective and distance correction with human faces is definitely one of those. So if you got the distance from the mirror correct, the effect might not jump out at you in person like it does with photos.
Camera focal length
It's not distance to mirror, it's the focal length. The focal length of our eyes is static
The "focal length" of our eyes is a subjective number, because our retinas aren't flat and our attention doesn't cover our whole field of view at the same time.
The numbers shown in that gif are the focal length, but the change in perspective is indeed actually due to the camera’s distance from the subject. When you are close to a person with a wide lens, their nose is considerably closer to the camera than their ears and hair, so it appears bigger. When you are further away with a nice telephoto lens for portraits, all their facial features are roughly the same distance away, so they all appear the same size.
Hair growing hack
Also you only ever see your face unmirrored in photos, even your phone's front camera will mirror the picture to not unsettle you.