From my atma experience, I believe the rng goes up according to the amount of people that completed the fate, not just hit it a few times and moved on to the next. I did fates when the atma began and when huge zergs were participating. My wife, myself, and everyone I knew got all 12 within 2 weeks. Now that it's died died down and so few are doing fates....I've gone 3 months without seeing a single atma on my alt.