Slush's pool is scored proportional and so is not much like PPLNS either.
So then how do we explain my math at the bottom of the previous page?
I don't have time to explain anything right now, or even look at your problem. But I just wanted to point out that you were looking at the wrong payout method before you spent more time on it.
There's a post in this thread somewhere that out lines the payout method, or you could try these: