@bobRaskoph and @mlucas are pushing you in the right direction.
Dramatica's Acts are part of the storyform. They are not necessarily the order that you watch a movie or read a book.
It's important to remember that Snyder is talking about screenplays and Dramatica is talking about stories. Screenplays start on page one and go until they are finished, about 110 pages. Stories start when an inequity becomes problematic and ends when things are put back into balance. Stories are not confined to a physical form, they are a mental construct.
That's a fancy way of saying that Snyder (et al.) are talking about how a story is laid out. Dramatica is talking about something entirely different, which is something like "how does this problem look from this perspective?" (For example, "How does my Situation of being blind look if I consider it from the perspective of The Future?")
Most of the time, the locations of Snyder's Acts and Dramatica's Acts overlap, but they are not the same. Melanie is not talking about Snyder's Acts.
Also, "Signpost 1" is a moment in, or bias towards some perspective inside "Act 1." You may be thinking that Signpost 1 is Act 1, but they're not the same.
Also, about when you introduce your IC. It is easiest to think of the IC as the actual character, or actor, playing the IC. But the IC is really the impact of that character. Which is why thinking about that character, or talking to a friend about the IC and remembering her fondly, is the IC.