The lowest upvote you have received from us in the last week shows on Steemworld at 0.13, while most are in the 0.20 - 0.24 range. Though if you want to track your upvote values with more accuracy (to eliminate the oddities of reward pool calculations and STEEM price swings) you should always make upvote size comparisons in rshares.
After HF21, we modified our upvote delivery so that instead of delivering only 20% of your pending upvote balance each time, we deliver up to 33% each time. This makes your upvotes more sensitive to variations in posting frequency. In your case, posting 8 hours later one day and at the regular time the next day resulted in a spike in one vote followed by a decline in the next vote.
We did announce in this post that the upvoting rewards will be reduced, but the change will be gradual. We have not made any other recent changes.
Alright, thanks for the explanation guys. I better read your posts more carefully ;)