It doesn't matter in summer so I put the notch down and toward the front all the time. If it is a solid cover notch up doesn't vent. If it is not a solid cover notch up will vent through the center of the hive which will not be good as the bees move up to the cover in the spring. With the notch down and forward the air coming in at the bottom vents up the front side of the hive (warm side facing south). That gives the hive the benefit of a vent without the possibility of chilling brood. In the south I suppose it doesn't matter what you do until you get a freak cold spell. I have had as many as three upper entrances in wintering hives and could not tell any difference between hives that only had the vent at the top. However, I only have 3 hives and that is not statistically valid for making claims.