The speed and spin you use as you hit a ball makes a difference.

Below is one of the things you have to take into account after you "bisect the angle" and determine the ideal rebound angle. When the cue ball strikes the rail while rolling (forward spin) it will retain some of that rotational energy and keep spinning the same direction as it was before hitting the rail. This causes a slight curve and change in the actual rebound angle making the ball go "long." Having some draw (backspin) on the ball when it hits the rail will do the opposite of the above and shorten the angle as shown below. Another factor which affects the rebound is cushion distortion. This makes itself evident when you hit real hard and the rebound comes up short. The most dramatic effect on rebound angle is side spin. Just a tiny bit can make you miss a shot. In fact. just the little bit of spin picked up by the cue ball brushing the object ball (collision induced spin) can affect the shot.