It is also possible that the best transmitting site could be at the edge of the desired viewers' area,and then directional transmitting antennas are a good answer.
Picture the various patterns a lawn sprinkler may be set to;sometimes you want a wedge,somtimes a circle or half circle. Or a cloverleaf,fat or narrow.
We had a radio station once that came in really well. The radio station then boasted that they were going to boost there power. They did so, but then we could not really get them anymore. The reason was that we were south of them and they decided that there market was more to the north. So they used a directional atenna. The result was that even though they increased there power- We were cut off from them. So I am kind of a skeptic of directional atennas. It better for those on the front side and bad for those on the back side.