Actually wall mounting a speaker properly and angled down provided a better soundstage that facing straight up. If you can imagine the waves coming at you, then a slight angle of 15 degrees or thereabouts will direct them to your listening position much better than say one that is flat.
The more critical thing is for you to mount properly - using the right mounts and tension. Make sure each speaker does not shake or vibrate when you tug at it lightly.
Thanks, very interesting comments!