I have purchased inner covers that have two different bee space dimensions. Why is there a difference from one side to the other and what is preferable? They also have a smooth side and a rough side, why is that and what is preferable again?
Unfortunately, not all manufactures use the same frame rest height. Some put the bee space on the bottom, some put it on top, and some split it between top and bottom. So depending on your frame height in the supers dictate which side of the inner cover you should have down. Make sure you have a bee space between the top of the frames and the bottom of the inner cover. If you have less, they will propolize it. If you have more, they will built comb in the space.
Correct bee space would be 1/8" in the inner cover. But most are either more or they are less. Most are wrong. :)
if you have 3/8" between inner cover and top bars you are good. use a tape measure to see which side of the lid to use.