Either insulate the knee wall and meet the insulation between the rafters coming down from the ridge, and then can leave out the ins. After the knee wall towards the eaves, or continuos insulation between the rafters from ridge to eaves and can leave out the knee wall insulation.
Will it not matter that not insulating right down to the eaves there will be only rockwool stopping heat/moisture exiting through the ceiling and up the sides of the insulated loft area.