I was going to say that Robo had a great and informative site about swarm traps, but I see he has been here already.
My own experiences tell me that availability has a lot to do with what home a swarm chooses. Dr. Seely said that they will choose the best location they can find.
I have had swarm boxes out about 1/4, 1/2 and 1 mile form my house that are the size of a deep, with old comb in it and lemongrass oil or commercial lures, and still had swarms move into used 5 frame nucs I had stacked in my bee shed. So to say the least bees confuse me about how they make decisions...
Having said that... going with the size you have is better than not putting out any swarm boxes at all!