I wouldn't use eifs down to grade either, but it sounds like he isnt. He's talking about rigid polystyrene, not the cured, white beaded board behind EIFS. I've only done the bagged, fibered plaster intended for polystyrene once, & I'm not sure why, but it actually does hold up IMO for some reason. I would see if you can get your hands on the plastic washers used for EIFS, as the washer closes over the screw head as you tighten them, & they "rough" so the plaster will stick. I've seen them sold with the tapcon already assembled from a insulation wholesaler.