That really is only a problem if the direction of the wind never changes. But if the direction of the wind turns around the farm stealing the wind and the farm being robbed of wind switch roles.
E.g. country A is saying that country B is stealing their incoming (upstream) wind, but there's currently a zone of negative pressure (based on the mountains/shore/passing by cyclone/whatever) on the country A's territory which actually allows for the pressure gradient to form through both countries A and B - so there's more energy potential available to tap into on country A's territory?
Areas with more changing wind patterns are likely less desirable.