IMO if the bees can plug the hole your usually ok. I keep mine to where the bees have to work through each other coming and going. Lost a couple hives last year to robbers but one hive right in the middle of the fray just ganged up and pluged the hole. Lots of fighting on the front porch but no bees got in. I've been really cautious this year with my opening size.
how wide is your entrance?