Yesodei HaTorah 2:5 Since angels have no bodies, what separates them from one another? They are not the same. Each one exists based upon the influence it exerts in a series of levels, one on top of the next. This is alluded to in Koheles 5:7, “…there is a watcher above the one who is high, and there are others higher still than they."
Yesodei HaTorah 2:6 When we say that angels are in levels one above the other, we don’t mean in a physical sense, like one person sitting above another. Rather, we mean spiritually, like when we say that one scholar is on a higher level than another. Additionally, a cause is considered to be above its effect.