Finally have gutted the rooms I am remodeling and am looking at materials for the transition between the room and the wall. As always a picture is worth a 1000 words.
The white is the foam vent on the underside of the roof sheathing, black is rock wool insulation (which will be coming out of the wall).
The attic has an R40 value of blow in in it, but the entire perimeter of this room (over 30ft of exterior wall) has no insulation other than the rock wool for the last 1-1.5 feet of the ceiling joists.
I have very little space to work with, the roof has a very low pitch and is a hip roof, which makes the outside corner even worse.
I understand the need to make sure I have air flow to keep the attic cold.
One possible option I have thought of is to use 2 inch XPS to create what would be similar to those foam vents, seal the XPS to the header, then fill the space between the foam and the Vapor barrier with the blown in material, then add more material to make up for the lost amount over the center of the house.