That's exactly right Adam. However, one of the 2 hives I am using for this has no supers on and the results are about the same. In this case the bees get into the grafting half by climbing over the dividing wall from next door, travelling along the bee space under the crown board. In both hives the half with the grafts end up with many more bees than the side without. I suspect though, that in the supered one some of the bees in the grafting half had come out of the super and had been intending to go to the bottom box but had been held in the grafting half box by the plastic sheet.

The grafting box is not only a long way from the queen but convection currents from the bottom box are diverted straight past it which must reduce the queen pheromone even more.

Steve (I'll give up on Rosie as my cover was blown long ago)