A method is described for improving the cooling effectiveness of a fluid which flows through a row of passage holes in a substrate (e.g., a turbine component), out to a high-temperature surface of the substrate. The method involves forming a slot over the holes, within the high temperature surface of the substrate. The slot can be formed within protective coatings applied over the substrate. Alternatively, it can be formed partially within the substrate, and partially within the protective coatings. Movement of a film coolant through the substrate and into the slot results in greater cooling effectiveness. Related articles are also described.