When summer is over and the hives have 1-2 boxes, I use size on main entrance 10 cm x 0,8 cm. Then one upper entarance in front wall. I may push my small finger to the hole.
So, that had been enough to my hives.
Many beekeepers are mad with their mesh floor. Like many say, it is "a modern bloor". Nonsence, it come with varroa and it is called often varroa floor.
if you have a mesh floor, you need not upper entrance.
We have in winter a proverb: shut the door, it is byed heat!..