In order to get in most efficiently you want to dive at just the right moment to get in while the ramp is still opening up.
For multiplayer runs, players should line up 2 on each side.
This works because the flaps on the side do not have collision, as you may have noticed when getting "stuck" while playing casually.
Another method involves clipping into the flaps as they are opening up in order to get even closer to the cabin.
If you leave the extraction zone right as you hear the words "Pelican-1 approaching pickup", but before the shuttle spawns in, Pelican-1 will hover shooting his Autocannon at enemies in his line of sight.
Any Helldiver who re-enters the zone will cause him to land, and any reinforcement can also sometimes force a landing even if the player steers out of the way.
Its a very powerful ability to use as a last resort or when playing casually.