Bees Choosing an Entrance

I picked up these bees last year in a subdivision in southwest London.  It was a secondary swarm - so it was smaller than a football but bigger than a softball--big enough that it was worth taking.

I call this hive Convenient because the bees were very good to swarm only 4' off the ground so it was very easy to collect them.

They been great and productive bees.  I was suspicious that the swarm may have come from an attic of one of the homes in the area.

This idea held with me because I noticed something funny, or say different about these bees compared to my other hives.

They would only come and go from the upper entrance.

I watched them for the longest time and every time I went to the yard they were always coming and going up top.  The bottom platform would be bare or nearly empty of bees.  There would be so many bees at the top they'd be piling onto each other and falling to the platform below.

Did they like the top because it was like the entrance (possibly attic) from their old home?

I gave them an inner cover with a centre hole and then an outer cover with an exit as well--this equipment I already had on hand--and it gives them two entrances at the top.

Now here's the stranger part.  The following spring these bees kept up with this habit.  We all know that the bees in spring would be new bees and that last years bees would be long since dead.  They would have even requeened too.

So why is this habit continuing?  Are they doing it because they don't like the bottom entrance?  Have they learned to go in and out that way from the older bees and so they're copying them?

More questions than answers but it's interesting to observe.

This year they are preferring the top as usual but I notice that they are guarding at the bottom and a few bees do come and go from there.