The knee wall doesn't have a top plate.  Each stud is cut to fit below a corresponding rafter, and a steel plate (recent addition) holds them together. 
With the metal plates, that connection will be good.


When I said "dead air space", I meant that fiberglass is supposed to be installed in a cavity with 6 solid surfaces around it ... not exposed to drafts.  If it's installed between the studs in our kneewall, then at the top it will be exposed to the drafts of attic ventilation while at the bottom it will have loose-fill cellulose pilled up against it.  I may be reading too much marketing comparisons from the other insulation types.
I wouldn't worry too much about this. You could just run the fiberglass all the way to your foam and let the foam be the cap at the top if you wanted.


Yes, I was planning on installing strapping between the two floors on the outside walls.  Not possible for the knee-walls, because they are all over open spanned areas of the house.  I'll need to find a fastener to positively tie the beams into the exterior walls.
Sounds good, just be sure the knee wall is well attached to the beam.