In game, you can jump onto a 64 unit box (if your FPS is just right). I don’t think player actually jumps that high, because you get the ability to go up a 24 unit step (?) for free. Even so, that gives you a 40 (over 3’ or 1 meter) unit jump + 72 unit player for a 112 unit minimum ceiling height. I find that 120 is a reasonable low ceiling height, whereas in real life, a 10’ ceiling is quite high.
For unrestricted movement in games like ET, you need to be able to hop around without hitting your head in the ceiling.
This shows exactly why building things to scale is bad for gameplay. The player representation and movement is simply too different from the way real humans move around.