Some of the hints as to how the body jumping/survival work can be found back in DAO when Morrigan is explain how she thinks Flemeth survives. She says that according to the Grimoire this has greater chance of success if the individual is already similar to the one making the jump, i.e. human and a mage. Then in DAI Flemeth says that the soul cannot be forced onto the unwilling.
So archdemon to Grey Warden results in death of both because the difference between the two is too great and the Grey Warden's soul resists the transfer. It works between archdemon and other darkspawn because whilst they are different in physical appearance, they are both wholly tainted creatures and the darkspawn are said to be soulless, so no resistance. Also any will they do have is controlled by the archdemon. It does appear to be an automatic thing with the archdemon having no control over which creature it jumps too, since the Dark Ritual is able to overcome the mechanism and re-direct the soul to Morrigan's baby. May be it travels easier to a creature with a soul than not and because of the natural resistance in the Warden, it goes by the easier path to the baby. (Morrigan has essentially created a short circuit in the system).
Corypheus to Grey Warden is successful because they are both humanoids, tainted and he already has some control over their mind, so they are effectively a willing host. What tended to be played down in DAI is how darkspawn are meant to be attracted to him in the same way as an archdemon, so really Cory running around on the surface should have triggered a Blight. Presumably the attraction to him is far weaker than that of an archdemon. It is also not clear but it must be assumed that he does have control over which tainted creature he jumps to. May be the fact that he still has a soul and seems in control of his mind means that he cannot jump to a soulless darkspawn or if he did, he would lose his autonomy and become a mindless drone too.
The Architect does present a problem. If we kill him, then there were plenty of Wardens standing there for him to jump to. In which case it has to be something that is done as an act of will rather than something automatic. However, he also seems to have no control over the Wardens, mage or otherwise, like Corypheus does. So either he does have to be aware of the ability and choose to use it, he isn't the same sort of creature as Corypheus or each Magister had different attribute they gained as part of the Blight.
It is possible that Corypheus realised the possibility of transferring only after the Wardens had found the way to kill the first archdemon. Dumat was killed in -203 but allegedly the Wardens only discovered the possibility of intelligent darkspawn in -191 when they captured Corypheus, which gave him twelve years to work out how it was done before capture and then a further 10 years while they were studying him, particularly as he could probably have influenced the Wardens guarding him into revealing the secret. They only finally sealed him away in -181.