If I:R makes 1 POP = 20,000 soldiers, then it can be something like every 20,000 soldiers die one POP dies. The same reasoning as VIC games.
Where are you getting that ration from? In the first screenshot they raise only 37k but the Rome they show would have hundreds of pops.
The point I'm getting at is that when you lose a soldier pop, which don't contribute to your economy all that much, its annoying but not the end of the world. Here you would lose pops that provide far more important things and you'd be fucked like. I like that there is pop-related danger now, but I also like the fact that pops being wiped isn't a sure thing.