I believe that those angle you are given on the sgaure for the side cut of jack or hip are the angles you would mark on the unbacked hip or the top of the jack rafter. When you cut them, if you are using a circular saw you would set it to 22.5 for the jack rafters and since you are making a compound angle cut across the face it would follow the mark you made on the top at the 28.75 deg.