I haven't read the code, but as I understand it, new steem is being added to the rewards pool at basicaly the same rate that the curation rewards are being given out. Similarly, your marble analogy ignores the fact that 7-day old posts are aging out of the pool at roughly the same rate that new posts are being added.
Since the number of rshares allocated for your post is constant and the size of the pool is (roughly) constant, the reason that the post's award appears to change is almost entirely due to the fluctuating price of steem.
If the number of rshares suddenly increased dramatically, the value of all other posts would decrease significantly.
I haven't looked into the numbers, but this could be a factor as well.
For instance, if the @freedom account started using all of it's voting power, every post it voted on would be worth a ton, and every post it didn't vote on would see a huge decrease in its payout.
True. I was oversimplifying. But those sorts of changes will tend to average out over time. My main reason for commenting was just to note that that the pending reward value can drift up as well as down.
You may be right....but if you are then it means the payout fade will stop now that it's been over 7 days since HF.
The reason I don't agree w the the theory that it's only because of Steem price is that the price went up last few days...until last night.