I used to ventilate under the outer cover until one year I opened the hives
on a warm January day and found that the cold air was condensing around the
inner cover hole and dropping moisture directly down on to the cluster.
Since then, I ventilate under the inner cover with 1/8 inch space (2 - 16
penny nails) That allows the moisture to exit around the sides or to
condense away from the cluster.
The 1/8 spacing seems to equal the same area as the inner cover hole.  I no
longer have problems with moisture
I have done this in Mid Ohio and the mountains of NC
Dan Veilleux
Vilas, NC