syntactic analysis - "MODAL + HAVE BEEN + ING VERB" expresses an ongoing action which finished or lasts from the past up to now?

There is a missing knowledge of Tenses in Modals in English grammar textbooks.

Ok, we know that "Present Perfect Continuous" is used to express a duration from the past until now.

Ex: They have been talking for the last hour. (the "talking" action happened 1 hour ago & continuously progress until now.)

Yeah, that's easy. But what about the structure "MODAL + HAVE BEEN + ING VERB"?

What meaning does the structure "MODAL + HAVE BEEN + ING VERB" carry?

See this example

• The baby must have been sleeping when I passed by his room 2 hours ago.

Does that mean "I am very sure that the baby was sleeping at that time (2 hours ago), but he woke up 1 hour ago"

or

Does that mean "I am very sure that the baby has been sleeping for 2 hours, and he is still sleeping now"

This page says "The perfect continuous conditional can be used in type 3 conditional sentences. It refers to the unfulfilled result of the action in the if-clause, and expresses this result as an unfinished or continuous action."

But what does "an unfinished or continuous action" mean?.

Ex: If she hadn't got a job in London (but she did), she would have been working in Paris (maybe still she is working in Paris now) (but she wasn't).

So "MODAL + HAVE BEEN + ING VERB" expresses an ongoing action which finished or lasts from the past up to now?

Note: could you please include a referenced source in your answers?