No real explination why one would beard more then any other. I use some solid BB and some screened, get about the same amount with either.
I have 1 hive that has been outside most of this summer. The photo I posted earlier in this thread, could have taken another last night but it would be the same photo.
A couple weeks back I checked in on them to make sure they had plenty of room and even moved some frames around to promote some more work inside. They accomplish the task that I set for them and still hang outside.
So other then they have room, nothing extra to look for. But they most of the time have plenty of room and just like to stay out where it's a bit cooler.