I don't think there's any truth to this - I have only just started the atma quest and the first two atmas I've received (Atma of the Crab in Western La Noscea I got from that escort FATE where you have to escort a Maelstrom messenger from Aleport to West Tidegate, which has absolutely nothing to do with crabs, and my second one was Atma of the Maiden from the Central Shroud, which I got from the FATE near Spirithold where you have to fight Charging Boars). Neither of these FATEs have anything to do with the Zodiac signs the atmas are based on.

So once again I'm pretty sure this is just another myth made by players who don't want to accept the bitter truth that the RNG of atma is exactly that - completely random.