All channels should be aimed with consideration for the center of the soundfield. This ensures people sitting off axis dont get all of one speaker and not the others. It is possible to create a realistic and centered soundfield for all listeners if this approach is used. Here is a vid that explains the details. Its kind of old now, but still very relevant.

Acoustics for immersive audio.

https://m.youtube.com/watch?v=DFbqJkjfABQ