I have hives with entrances from 12mm x 9mm bee width to hives with entrances about 15 inches long x 9mm high. The bigger the hive, the wider the entrance I use. I don’t worry too much about bearding in this hot weather; it’s natural. I have lost 1 nuc this summer that oddly enough had about a 3” wide bottom entrance. It was robbed out, but I’m not sure if the robbing occurred before or after colony was lost. I didn’t see robbing, but I don’t look everyday and robbers can kill a colony quickly.
I think the best solution is to move small/weak colonies away from your strong ones. If that isn’t possible then I would not hesitate to narrow down the entrance to 1” wide or less. Just keep narrowing until you see the problem subside. If you’ve got a ton of bees bearding around a smaller entrance, it certainly makes it harder for wax moths to get in and probably makes it harder to robbers to navigate too.