Thank you Lal:
– However, an Ariya will NEVER grasp a lower bhava, because he/she has REMOVED anusaya at that level. For example, a Sakadagmi will NOT be born in the human bhava or the apayas.-
This refutes both 1) and 2) in my post. Of course, a Buddha who takes on a human form after leaving the Tavatimsa is another concept altogether.
No doubt I will ask further questions as they come up
ever grateful