I know this probably won't stick, but I nominate "eye-exit pupil alignment (@correct eye relief)". Takes longer to say, but it eliminates the "box" out of "eyebox", bcuz there never was a box anybody was looking at/into.
A scope might be considered "the light at the end of the tunnel" but you're not even looking at that until you get to the correct eye relief, and when you get to the correct eye relief, there's no tunnel.
If there was some kind of finite structure like a box, then it wouldn't change size as it does when it goes from a small "white spot"/Ramsden disc/exit pupil in a "sea of black" transitioning (and getting larger) until the exit pupil is filling the eyepiece when you've got the scope lined up on axis to your eye.
What you're seeing is the changing dynamic/"out of whack"-mis-alignment of 2 optical systems until they're lined up on a common axis and the "dance" bet. the exit pupil and your eye taking place outside of the optic.
A long time ago, somebody looked through a scope before it was lined up right and thought of a box (it would have to be a box that changes size), and he must've been drinking Jack Daniels bcuz a box is square (or a rectangle) when we're talking scopes/a round tube.
Coming from photography over to the scope world, the difference seems to me to be that using scopes is harder/kind of "messy" since you can't fasten your eye to an eyecup behind the camera which helps to line up your eye to the image/exit pupil.
It's no "biggie", but it's there.