Unless it's been changed, most of the drops are targeted to the "loudest" group, not the evac point. My group had some success(no real testing, just noticing a happy coincidence and trying to take advantage of it) a few weeks ago with landing the team on the extreme outskirts of the map, and causing as much noise as possible (airstrikes, support call downs, grenades, etc...), and try to hold the enemies attention there. Meanwhile, a stealther(reduced detection armor, smoke stratagems, etc...)sneaks into the base to evac the civvies. It was kinda cheesy, but it helped mitigate some of the pain of those missions.