This is not only caster problem, melee have this problem too. This is because this game dont have 180° attack radius but around 60° - 90°, if you add real game delay around 400ms (dont mistake this with ping) then you have to aim infront of running ppl. Auto-face will not work every time if your target is moving fast too close or when just runing straight through you. Only advice to counter this is simple aim manualy infront of targets like in battlefield or in any other fps that dont have hitscan detection