Where are you located Jason?
I've got mine set at the 4" slot and there are days when I feel like shutting it down more. It's been hitting 80 here the past couple of days and down to 50 at night. 3 of my hives were in NUCs the other day with a 1/4" x 2" entrance and one I had stopped down to 1/4" x 3/4" because I wanted to make it easier for them to stay warm- it was a weak colony.
I was looking at the hives today and the bees looked happy- no traffic jams at the entrance, no bees fanning to ventilate, and plenty of bees flying and coming and going. I'd say my entrance is about right for right now.
I'd say, if the bees are really piling up outside and there is obvious congestion at the entrance, open it up, especially if they're fanning to stay cool. Here in Maine, I imagine I'll probably go to an 8" x 3/4" (1/2 open) opening next month and leave it there for July and August unless we get a really hot spell and the bees make it obvious it's too warm inside in which case I'll open it up more. Remember, they want the brood nest to be around 93 degrees so when it's 70 during the day and you think it's hot out, the bees are probably thinking it could get a little warmer...
The average May temperature here was mid 40's at night, mid 50's during the day and it rained 25 of the 31 days. I had my entrances stopped right down. I only opened them up some a few days ago.
I guess the best advice I can give you is to let the bees tell you, by their actions, if the entrance is too big, too small, or just right.