LotR -- Book 6 - Chapter 2 - The Land of Shadow

[Kuruharan]

But, as a reader, I know that Gandalf knoweth not the will of Eru: he was making a best of an educated guess as he could.

What does what Gandalf may or may not know about the will of Eru (and I think it rather presumptuous to assume what Gandalf "knew." He may have been limited but he always "knew" more than he told.) have to do with the nature of the Ring?

In other words, why leap to the conclusion that it was the ring's idea? That could happen to any evil ring that is worn by someone not wholly evil. Would shrinkage happen to an orc? Wraith? It's sentient enough for rejecting wearers only? Why would it not slip off every finger all the time?

I'm afraid this makes no sense. You sound like you are making an argument in favor of sentience, that the Ring is trying to pick its spots.

I just think if it's that sentient, it would have found an orc in the Misty's somewheres and eventually rolled itself back to daddy S

Not necessarily. Sentience does not imply all-powerful, any more than any other character in the story is all-powerful. The Ring is extremely limited physically, it is after all...just a Ring (as you pointed out earlier). It does require a bearer because it has no arms and legs. The Ring can attempt to abandon a bearer, but it has very limited physical tools to accomplish this. The Ring probably thinks it is more effective to attempt to dominate the bearer so that the bearer will do its will.

See? My point here is that look what conjecture does. Why is the ring a "he", and not a "she"?

If you want to go that way...because Sauron is a he.