“Where, however, there is a paucity of satisfactory direct rental evidence, then the best evidence as to rental value is likely to be the “indirect” evidence provided by the gross values of similar hereditaments; and the greater the similarity between these other hereditaments to the particular hereditament in physical respects such as the nature of the property, type, age, design, size and surroundings, the better is the evidence so provided. Should there be available as comparables a number of hereditaments all equally similar to the particular hereditaments in all material physical respects, then those which are in the same locality as the particular hereditament normally provide better evidence as to rental value than those which are in some other locality, because the former are more likely to be in similar economic sites and therefore the more truly comparable.”