bearding is normal when the temps get hot. my hives sit in 32 to 38 degree in the summer and they are fine. if it is hot, i do as you have done, and prop the top open just a bit. i do not think you need the netting. if the bees come and go through the top, it does not matter. the only time it would be a problem is if other bees are trying to rob that hive.