In blowing cellulose insulation into exterior walls that have some thin (1/4 in) insulation with a kraft backing already, where should the new insulation be blown? Between the insulation and the sheathing? Between the Kraft backing and the plaster? Both?

I would like to keep the vapor barrier on the inside of all insulation, but this is leaving a lot of unfilled space in the wall since the existing insulation is nailed to the sides of the studs and lies right up against the sheathing. The backing won't expand enough to fill the whole space.