I don't think the angle adds anything, but I'm a noob myself...
I just used REW to help me eliminate the nulls by running the generator and real-time monitor, mic was placed at MLP and I was also sitting in a seat next to MLP to actually listen to the sound pressure, and fine-tune with my ears.
I still need to hang my surrounds, route wires in walls, and re-run Audyssey.
How high is recommended to hang the surrounds (sides and back)?
Generally accepted is surrounds should be at head height when sitting or slightly above and back surrounds about 3 feet above that.