Student or Learner
Is "on top of" physically above or very close to each other? I guess the latter.
ex)How do eight million people in New York function, live, work, and even thrive on top of each other? ...Whether they are from Ireland, Italy, West Africa,...it's that mix of people and cultures that has always been the city's most solid foundation and source of energy...
It's common to say of people who live in cramped houses that they "live on top of one another."