The watch towers will give him less benefits. When comparing two province you have to give them the same tpa other wise it is much like comparing apples and oranges. A non-dwarf with 1tpa and a dwarf with 1tpa that how you should set up the example. However I will use your example, inherently the dwarf had to keep and maintain .43 more tpa than the other non-dwarf province in order to reach the same benefits from tpa. Because he has the same benefits from tpa the dwarf will have the same benefits from watch towers. In fact if the dwarf keeps his or her raw BE at 100%(130%) the watch towers will do more for the dwarf. Howerver when dealing with provinces with the same modtpa the dwarf will always be at a disadvantage and thus watch towers will be less useful.