blast cannot be directed ..... only an object in front or around the explosive filler can be directed by the blast an example of anti personnel Claymore which directed the shrapnel liner or Shaped Charge (copper liner) and in case of ERA (Flyer Plate), if you put ERA on thin armored vehicle, their very thin armor plating itself would spall the vehicle armor and become another "Flyer Plate" for the crew inside the vehicle.I don't think it will cause problem, most of the energy/ blast of the ERA explosion will be directed outward.