Those curves you posted are very impressive. I see the target curves for the front M5s are downward tilting. ARC therefore must be determining the designed response of the speaker and attempting to correct to it for your room. All indications are it did a marvelous job. Does it allow you to adjust the target curve slope?
Not sure if it detects the downward slope, or if the smart guys at Anthem just recognize that response should naturally slope off. I haven't played with it a ton, but I'm pretty sure you can create your own house curve for ARC to correct to.