Identify your use: topping (browning), filling (salt + bite), or baking/melting (needs good grate-and-go behavior).
Choose the closest match from the list: aim for a semi-hard, salty, nutty cheese for the most kefalograviera-like outcome.
Apply the listed ratio. If your substitute is saltier (like Romano), start slightly lower and adjust seasoning in the recipe.
For baked dishes, grate substitutes fine so they distribute evenly and melt without pooling.
Taste after the first bake cycle (or during final minutes). Add a small pinch of cheese or salt only if needed.