By nature I am often demanding, but I didn't read your first reply as didactic.
"Susan began to tremble, since now John had become very angry."
What do you see as the difference between the later examples that are teamed with "since" and the example above, which is also teamed?
And would you say that "since" appears here in its conjunctive meaning and not as an adverb?
Discursively of course.