Insulating kneewalls with obstructions – GreenBuildingAdvisor

I’ve got knee walls in several rooms of my 1990s era zone 5 Michigan home. See photos attached. At present the 2×4 bays are filled with R-13 faced fiberglass batts. A thermal camera shows these rooms are losing a lot of heat through the knee walls, particularly at the ceiling and floor level. 

After much reading of Martin’s articles, my plan is to screw 1.5″ foil-faced R9.3 polyiso to the joists and to seal around the edges with canned foam. However, the joist bays are obstructed by what I believe are structural supports for the roof. How should I apply the polyiso boards here for maximum thermal efficiency and minimum labor? Should I cut them to fit between the structural supports so they can be placed close to the fiberglass, or is it possible/desirable to attach the boards to the structural supports? 

Additionally, for reasons unknown one area of the knee wall doesn’t appear insulated, but instead has home wrap. Any thoughts on what might be going on there and how to address that area? 

Thanks very much