I don't have a definitive answer to your question but I had a similar situation last Spring and I placed the swarm hive that close to the original hive. I was not as brave as you and just left the cut branch on top of the brood box.Covered it with an empty deep box and put a top on there. Later most of the bees had left the branch and I just placed the branch in front of the hive. So perhaps it was the shaking rather than the proximity to your other hive. Susan