I had one with 1/2" x 6" open perpendicular to the bars right under the bars, one with 1/2" x6" opening perpendicular to the bars at the bottom, a barrel hive with a bung opening at the bottom. All seemed to work fine, but I seem to like the upper entrance better as they seemed to fly earlier/colder that the other ones. Granted with the limited sample size, I can't really draw any conclusions.