Ah I found it..http://www.bbka.org.uk/freefiles/diy_open_mesh_floor-graham-white.pdf
HOW DOES AN UNDERFLOOR ENTRANCE WORK?
The bees fly into a covered vestibule which is a sheltered space about 4 inches deep and four inches high, running the full width of the hive. They walk across the landing board and climb the rear vestibule wall to enter the hive through an 8mm wide vertical slot that runs the full width of the mesh floor.
The advantages of this are that:
â€¢ No rain, wind or draughts can blow directly into the hive front
â€¢ No mouse-guard needed; mice cannot climb up through the vertical 8mm slot
â€¢ Wasps and robber-bees have a harder time getting in; they have to pass the guardbees on the landing board and then climb up past more guards above the vertical slot entrance.
â€¢ A simple wooden block closes the hive completely
â€¢ No ventilation needed when moving the beehive.
There is no mention of wax moths, so that was my thought, if something like this would possible reduce wax moths from getting into the hive..