I talked with a beekeeper today who manages 1000 colonies. He says anything more than one deep is too much room , and then puts an excluder on this single brood box. My experience is that the bees need more space. My mentor when i got my first bees in 2008 told me two deeps were standard, or two deeps and a medium, depending on time of year. I tend to make sure the bees have enough room and that means at least two deeps. (I don't use queen excluders.)I don't see how a strong colony can build up in the space of a single deep and not swarm -but this beekeeper said they make a lot of splits (to sell or to cover winter losses) so maybe that's the reason. Would be interested in hearing thoughts on this.