Siebe said: “All three kinds of contemplations are meant, do you agree Lal??”.
Yes. Most people get the breakthrough with anicca, some with dukkha, and fewer with anatta, as you mentioned (based on their gati).
But the key point is that when one grasps one of those, one grasps all three withing a short time. They are intrinsically related to each other.
And then it will never be lost, even in future lives. Just like a child who learned how to add will never lose that capability, the Three Characteristics of nature (Tilakkhana), once grasped by the mind, will never be lost.
Then one’s thinking process will be AUTOMATICALLY driven by that perception (sanna) about the world of 31 realms. That is what is called “Samma Sankappa” (how “right” mano sankhara automatically arise).
Then one will start generating vaci sankhara and kaya sankhara BASED ON such automatic thoughts. But that will happen in stages. Only “apayagami thoughts, speech and actions” will be stopped automatically for a Sotapanna. He/she will still need to control “kama sanklapana” with own effort, if to be released from the kama loka, etc.
Therefore, it will be optimized only at the Arahant stage.