I think a few of the more important questions are: How old are the cats in question? How long have the boxes been in the spots where they are? How much of a routine have the cats been used to? The older the cat, the longer the boxes have been in that spot, the regiment the cat is used to..... all have a role in moving boxes.
In my case I have 5 cats in the house, 3 boxes. I break all the "rules" because they are all close together. I have not had any issue with them using anything but the boxes unless there has been a diahhrea issue (only once). But my cats are all under 2 years old. Very young and adaptable. If your kitties are older it may be hard for them to adapt to the change. Just my thoughts.