Adding insulation to batt insulated rim joist cavity – GreenBuildingAdvisor

Have a 70’s home with batt insulation in the rim joist cavity.  It appears they installed with the insulation toward the outside of the home and a foil backed vapor barrier toward the inside. which is what I can see.

I have been going around re-insulating rim joist cavities with 2″ foam board and great stuff.  However, I had to run some new pipe above a bulkhead and have access to a bunch of these rim joists that are insulated with the batts, but my access is really poor to the point I don’t know if I can even get a 2″ piece of foam board installed much less seal seal the perimeter with a can of foam.

Advise on what to do?  Add more batts behind the vapor barrier of the existing batts?  Tear out and add thicker batts with the vapor barrier facing toward the inside?  Add foam board behind the existing vapor barrier?  

Thanks