We note in passing that the value of ϵ s is dependent on how scaling is constructed. We expect different ϵ s and scaling behaviour when a scaling line is constructed using just a single metal with varied facets (V 2 ak is a constant for a fixed metal, rather than = f (ϵ d ), see SI Section IV for further discussion). Since scaling lines are, in general, constructed across metals, we emphasize this type of scaling in this work.