I would like to share the idea of upper entrance.
If I were a bee, I had to go through from the bottom, 2nd and 3rd box with full of heavy nectar, I would be very tired of climbing all those crowded places, the structure made by human being just like a file cabinet structure, no other entrances like the natural environment. So, it is great for bees to have an upper entrance, hassle-free.
Anybody who has different idea, please share ~
Thanks in advance ~