Antenna radiation characteristic

I am getting ready for my exam and I am confused about radiation characteristic of antennas. I have a two way propagation (LOS and NLOS path). my transmitter antenna has characteristic as cos(teta). How this radiation characteristic effects my calculation for Elos or Enlos. Can I say that radiation characteristic equal to the directivity? Can I write Pradcos(teta) or ENloscos(teta). How radiation characteristic affects the path loss?