My room is 13ft by 20 ft with 8 1/2 ft ceiling. I understand that I should have the L/R speakers at the same height as the center speaker and these three speakers aimed directly at the seating position. I understand that the L/R surrounds should be on either side of the seating position and about 2 or 3 feet above ear height and aimed straight across the room at each other. The rear surround will go on the rear wall. I understand that about 6 1/2 ft elevation is the ideal height and it should be directly behind the seating position. This rear wall is about 3 1/2 ft behind the seating position. My question is, do I aim this rear speaker directly forward or do I tilt it down to aim directly at the seating position?