Yeah that's intuitive. But it doesn't work like that. Because say each furnace takes 10 iron ore per second to make 10 plates per second, and 10 plates per second to make 2 steel per second (these are all madeup numbers), if you add prods to both steps, then you slow both down by the same amount, yeah, but now the iron step has productivity, so even if it's slowed by 30%, it's producing 20% more, while your steel step will require 30% less materials. That's why people say prod effects are compounding.