Re: Entrance reducers for winter?
I'd close the screened bottom board by inserting the plastic piece.
You need some hive ventilation to exhaust moisture and provide fresh oxygen. Can be done by an inlet of the opening in the reducer at the bottom. Need an exhaust port. Can use the inner cover with rim up, but you need the center oval open and the 1 1/2 inch opening on one end of the ridge also open(Telescoping/outer cover should not be blocking it).
Dead bees blocking the bottom entrance may not be an issue as you get flying days and undertakers can rewmove the dead bees. However, if you are at all concerned about dead bees blocking the lower entrance or if it's a problem, flipping the outer cover, so the ridge opening is on the under side, works to provide oxygen when the bottom entrance is blocked.
If mositure buid up is a problem you can add pop sicle stick width shim to taise the outer cover to provide a vent. Can also add a popsicle width shim under the inner cover edge to provide a bigger exhaust vent.