@Packrat just because a Brigade has 5 times the troops does not mean it has 5x the efficiency or efficacy of a unit with less troops. A single trooper has a finite amount of power. Just because you have more of them doesn't mean you have more absolute firepower. It means you have the potential to apply that troopers firepower more often.
For example: If you have guys with spears and hide shields vs an M1 Abrams Tank, it doesn't matter if you have 5, or 500. The 500 still are probably going to lose it's just going to take more time and ammo to get through them.
So you're left with a couple of choices depending on how accurate you want to be. You can (and should) beef up the health of the unit, there are more bodies after all in a Brigade then a Platoon. You may wish to bump up the applied damage a /little/ depending on if they get additional more powerful hardware (Like say mortars instead of just rifles and hand grenades) depending on the amount of troops. Or you can ramp up the 'Number of Attacks' while keeping the damage low.
If one trooper has no chance of defeating something's armor (Or very little) then 1000 troopers with identical gear are still not going to have any better chance at it. But there would be a lot more /chances/.