I believe it is fairly common. I have the same situation. They utilize about a one foot section on the right side of the tank and simply fan out beds in the sand in the front and rear corners. The BTA has even (at one time) postioned himself in the one corner and the clowns wanted nothing to do with him.
Not sure whether they are lazy and do not want to deal with the flow, as well as its where I always feed the tank. As long as they are healthy do not worry, they will venture out eventually: for a few seconds that is