It's the other way around. yts goes up as the posts are made a greater and greater distance in the future from 12/08/2005. That means that the ratings of new posts are pushed UP, rather than older posts being pulled down.
Yeah, you're right. I simplified it since posts falling down is easier to conceptually understand. New posts start out with a higher rating, and an old posts needs to boost its rating 10x to be at the level a posts starts out at 12.5 hours later.