Sorry Runemist,but one box for 3 cats is just not enough.
I have 3 cats and I get away with only 2 boxes,because they are larger Rubbermaid storage-boxes.
Mine are downstairs,side by side.
You don't have to put them in different areas,but you definetly need more than one.
"The cruelest animal is the Human animal"
3 kitties,Rocky(r.i.p my boy),Chico,Vinnie