For 3/8" I don't feel you need to reduce, not on what I assume is a production hive. I got some hives with bottom where the entrance is smaller than 3/8" by a bit and only half width of the box. I thought it was a good idea til it gets hot then the hives bearded heavily even with 3/4" hole in the boxes for other entrances. Just can't move enough air through that little bottom even with afternoon shade.