Last year I added slatted bottom racks to all 3 of my hives and the bearding virtually disappeared overnight.
Yesterday, because we are in a dearth and I was afraid of robbing, I cut my hives entrances down by half after having them wide open since spring. Tonight at dusk I noticed the most bearding on all of my hives that I have seen since putting the slatted racks on last year. I am surprised what a difference in ventilation reducing the entrances by half made. I guess tomorrow I will crack the tops a bit to see if that helps with the air flow.
My bees are like yours ldaxon. When I put a slatted rack under the brood nest, bearding goes way down or is eliminated. I'm guessing the slats make room in there for the field bees to roost at night? When I have a smaller bottom entrance, the bearding goes up again. Changing the size of the bottom entrance has a big effect.
I have some hives running with bottom entrances and some with top entrances. I get way more bees hanging out on the landing board in my bottom entrance configurations than the top/mid entrance hives.
My hypothesis is a top entrance hive can be more easily ventilated by the bees since heat rises. I think the top entrance setup also gives the field bees lots of room inside to roost. However having a bottom entrance covered with bees at night is good at keeping moths out.