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