Question about the form of the ghosts (spoilers)

There are several different presentations of ghost-state in the movie.

Ghosts in the forbidden rooms retain a human-like physical form, only expressionless and sickly pale.

Some are dark shadows, wandering around, staring at people.

Some seem to be a mere dark spot on a solid, like the spot left by the woman jumped from the tower, crying for help.

What do you think are the exact criteria for entering each state? I am curious about this because while either one of these forms of afterlife is bleak enough, the third one appears to me infinitely worse - locked in a space that is as large as your own size forever, as opposed to being able to move in a room and wander around, and have contacts of some sort with others ; so I think the difference matters somewhat for the movie's portrayal of the loneliness of the dead.

Lastly a closely related question: the spot left by Junko was subsequently "cleared" by the wind. This, plus the statement "so I'm going to live...all alone", occur to me a hint that she, having realized the eternal loneliness in both human and ghost "lives", somehow found a way to instead be totally obliterated; any thought on that?

BTW this is my first post here and I'm not a native speaker; sorry if the language is not too clear!