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Okay, so... Both. I don't know how to explain it though.

The AMOUNT in the reward pool is based on a 30 day average of something. (I realized tonight, I am not sure what..)

The rewards themselves are paid out on a 7 day calculation having to do with voting stake. Geez, don't try to repeat that.

I get how it works, but I can't explain it. lol

Looks like you may be right unless HF 20 changed things.
https://steemit.com/steemit/@upbuzz/understanding-the-steem-rewards-pool