If your going to get serious about swarms, then order a book from Root publications called "Swarming", item X56. It covers not just good information and practical tips, but goes over years of swarm research by the likes of Bonney, Morse, Ott, etc. Much of the research they make reference to was from Cornell. Not a big book, only 62 pages.
Tells you like the "optimal" height....8 to 10 feet.
Size of trap....little bigger than a deep.
In side by side tests, they can show a distinct bees preference to things like a bottom entrance over a top entrance, a south facing entrance as opposed to a north entrance, a shade location over a sun location.
Even talks about first year queens swarming less than half of older queens.
Not based on a bunch of opinion. Based on side by side test, and research. Very informative. The book shows very clear preferences that the bees have, and what gives you the best chances of getting swarms.
You can order by calling 1-800-289-7668 The book last year was 5 dollars and included shipping. Well worth the money.