IMO - green area is for a general lung/heart broadside - red dot would be high shoulder (spine) shot that (some say) should drop the buff on the spot (it wouldn't be my first choice tho)

Also you may check the following site - go to buffalo then scroll down for shot placement and trophy judgement...

http://www.safaribwana.com/ANIMALS/indexanml.htm

P.S.: IMO on frontal brain - aim between the ears (no matter the angle of the head)