The checkpoint in Miami seems to open and close during the day. In Feb while departing to SDQ, I went to the special boarding line only to be told that due to the departure of too many flights at one time, the line was closed. Of course, the sign was still in place indicating that this was a line for AAdvantage elites. In MIA, the better solution seems to be to walk past security between the E and the A terminals, usually one line is fairly short. Once you pass security, these terminals are interconnected. Just remember that the presence of a sign does not mean that you can actually get in an elite boarding line.