Are slat racks less efficient at creating a dead air space if the racks run parallel to the frames instead of 90 degrees to them? Just seems to me that debris, mites, etc would be more prone to fall through if they were parallel to the frames.
I prefer the slats run the same way as the frames. Yes it does create a dead air space between broodbox and bottom board that acts as insulation.
The slats I designed uses dowling instead of flat stock for the slats which allows more bees to cling to the slat and do useful work and helps mites, wax debris, etc, fall out of the hive.