I think it is related to posts with recent payouts. I checked other accts and all have the same results. Anything recently paid (maybe in the past 24 hours) are earning higher rewards.
I checked someone else’s post with a reward from 3 days ago and the reward was less; similar to the Tim Cliff post from this acct.
Stopped researching since it’s past my bedtime. Let me know if you find out anything @simplymike!