I think you have to go landside. A through E low are linked airside, for E high you have to go outside security but E high is rarely used since D opened. Probably more AA flights use D than C, but last time I looked you couldn't get to H airside (however I wasn't looking hard). The security lines at MIA vary from 5 minutes to 2 hours, depends on the time of day, the cruise lines and a few other factors. It can go smoothly but often does not.