So I really enjoy the 'Defend/Rescue missions' and in the most recent one I've played the Resistance soldiers were real badass. After I rescued the first group unscathed, they basically handled 5 enemies at once by themselves. Their damaged having been bumped up from 2 since the beginning of the game to now 6. I believe they also have more HP now.
So what affected this upgrade? Is it over time? Because I had a Relay in that region? Because some tech I unlocked gave them better weaponry? Can they get even better?