re: Answer Is Probably Related To Location
Certainly the areas in his papers used to support this are all heavily cratered old upland terrains. Interestingly the papers by Hartmann I could find call talk about the relationship holding down to ~10 m, not 1 m. Perhaps the journalist got it wrong, or it was a slip pf the tongue, or there is some as yet unpublished data. Maybe I have not found the right paper yet.
Jon