Claire asked me to post what I do to provide just a tad more ventilation to my hives.
What I do is very simple actually, I just raise the top cover up and slide it back and rest it on the inner cover exposing the notch in the inner cover that allows a 3/4-inch hot air escape.
Of course, I have removed the bottom board and my hives are raised up about 18 inches so plenty of cool air can get inside via the screened bottom board.
It used to be that the inner covers came with a notch, but the ones we buy at the Farm Store lately do not. So, you should (in my opinion) cut the notch in. With the right tools in your tool box, that is fairly easy.
See attached pic. and as you will noticed, bees can and do go in and out of the small hole. Not too much, but they do.