In RET, the reason a flat map is distorted is because the real world is spherical, which is impossible to flatten out without distorting it.
If the Earth were flat, there would be absolutely no distortion. Projecting a flat Earth to a flat map will have no distortion. The distances should all be perfectly accurate, even though they can't be on a globe. We've measured Australia. It's a lot bigger than your map shows.
The dimensions beyond the third are tiny and have practically no effect. Also, they might not exist.