Hmmm .... Well if they are already in full view of each other I can think of four possible basic solutions: improve the weather/time of day; increase the skill of all loons; improve the waypoints; or if all else fails beat the game over the head with a reveal command...
"Westgrp1 reveal _x" forEach units Eastgrp1
Syntax not guaranteed.
However, if I were you I would change the setup. Have the enemy group on a hold waypoint in the middle of the town: as the chopper approaches they "hear" it and come to investigate. In other words use a switch trigger to put them into a seek and destroy waypoint close to the chopper landing spot. This is going to look much more realistic than if they just stand there watching an enemy chopper land 30m away without doing anything about it.
Playtest it until you get the distances and angles right, but the idea is to have the enemy running towards your group as you disembark. Because they are moving it will be much easier for your group to see them.
A few enemy should remain in the town: perhaps medics, drivers, cooks, clerks, etc - poorly armed and lower skill.