Does everyone get in? No. Even people with Fast Pass are told they can be shut out if not on line at about the 30 minutes before show time.
We don't mind sitting in the back. If not, how far in advance should we line up? Between 30 minutes up to an hour prior to the show.
The day we are going is a crowd eating of 4 and there are 2 Fantasmics (7 and 8:30), we are planning on the 7pm.
Rule of thumb is that the earlier show is more crowded. And if you are so inclined, best seats are granted to those utilizing the Fantasmic Dining Package.