Maybe I wasn't clear in my original post.
Silhouette scales well from individual to squad/vehicle battles and everything in between.
Which is ok for RPG, usually. But keep in mind that the wargame version of the same rules are squad-level, not designed to tackle larger scales like battalion level or strategic.
It allows your party to man a WWII bomber and fight against 6 Luftwaffe fighters as easily as it allow your PC to fight vs. 3 NPCs or one AT-AT walker to fight vs. 4 landspeeders and 1 Jedi. And it is pretty efficient in handling 5 PC vs. 12 NPCs, too. But it is not designed to scale up to "large-scale battles with multiple thousands of combatants".
Note that in my original post I mentioned squad based. I.e. Silhouette allows you to model interaction (fighting) among individuals or "units", where a unit is either a squad of infantry (6-10 people, I believe) or a vehicle.
Silhouette has two "scales": "individual" and "vehicle" - if you have to mix those, you have easy adjustments to move from one scale to another (for example damage at the vehicle level is multiplied by 10 when applied at individual level targets, because vehicles mount bigger and more powerful weapons, at the same time, you can perhaps disable a truck with a single well-placed rifle shot, but you must roll pretty well because your damage will be divided by 10 to find out if it affected the truck).
This won't allow you to easily replay the Battle of the Bulge, for example, because instead of modelling 250000 NPCs (just for the Allies) you'd have to deal with 25000 "squads" which is not a big improvement.
There may be extra rules for larger battles, not sure. But it's not part of the core, and it's not very different from other "mass battle systems" that have been designed for years.
Please understand that the "sweet spot" for a RPG is, at most, squad level, because in an RPG we care about our own PCs, as individuals. And for that, Silhouette (IMHO) shines.
If you move too far on the size scale, you end up with dry tables that reduce the whole battle to a couple of dice rolls, plus an "consequence roll" to see if one specific man was killed, wounded or suffered no damage after his brigade has been obliterated by enemy forces.