I have preferred the slats running the same direction as, and directly under the frames like the Betterbee version. The reason is I use screened bottom boards to help with mites. If you have the slats the same direction as the frames, the mites can fall straight through. If you have them run crossways (perpendicular) to the frames, it cuts down by 50% the area the mites can fall through. Instead they land on the part of the slatted rack crossing between the frames ,and then climb on another bee. That defeats part of the reason for the screened bottom. If you run a solid bottom I guess it wouldn't matter.