Greg is, once again, 100% correct on this. I have torn this detail apart on at least two homes, and was blown away by how much evidence of air movement was evident. This included black streaked fiberglass ceiling insulation that looked like a filthy furnace filter, and mold growth on top side of the sheetrock, at the ceiling edge. The area needed to be properly insulated, and tightly sealed, for the building to perform well.