Cats need vertical space. It is especially important in a multi-cat household where hierarchy is a big deal. Generally speaking, your "top cat" is going to be in the highest spot of your home, where it is easy for them to survey their domain. It's far more involved than all that, and there are plenty of other ways cats display dominance, but elevation is a basic visual cue.
|Mona on the staircase.|
|Some boys enjoying a multi-leveled view.|
|Cats on every level!|