My guess is that you turn at the time from MIA. If you didn't have any great tail wind or anything you end up turning inside 6.4D and can descend below 2200 as soon as you are established on final. On the other hand if your timing took you beyond 6.4D due to a high tail wind or whatever then you must wait until 6.4 D on final before descending below 2200'. Clear as mud.