All our airports have a loading range from 10 NM to 16 NM. The only exception is JFK, which has a loading range of 7NM, in order to save memory and fps due to the close proximity to LGA, so we don't load JFK when the sim has loaded LGA too.
Loading at 3NM simply cannot happen, and there's nothing in the software that could reduce the loading range of the airport, not the main buildings at least.
You can increase the loading range of the smaller objects using the "Anti pop-up" setting of the Addon Manager so, at the maximum setting they will all load together with the main buildings, up to the maximum range of the scenery ( 7 NM at JFK ), but the main buildings will always load (at JFK) at 7 NM out.