As far as I know, below something is like saying that one thing is physically under something else because it’s beneath it. But I’ve come across what looks like a different usage of the preposition below in this sentence from George Orwell's 1984 (emphasis mine):
All good things in the world of Oceania today, all knowledge, all happiness, come from Big Brother. Nobody has ever seen Big Brother. He is a face on posters, a voice on the telescreen. We can be sure that he will never die. Big Brother is the way the Party shows itself to the people.
Below Big Brother comes the Inner Party, which is now six million people, less than 2% of the population of Oceania. Below the Inner Party comes the Outer Party. The Inner Party is like the mind of the Party and the Outer Party is like its hands. Below that come the millions of people we call 'the proles', about 85% of the population.
This is confusing because it does not use the preposition below with the “under” sort of meaning that I have been taught. Does below have other meanings that apply here? How could it have been written not using below so that uses a word with a meaning I already understand?