When I up-vote, the reward payout actually goes down!! WHY??

Hey... Does anybody know why the reward payout sometimes goes down when I up-vote a posting? It seems to have no rhyme or reason why it goes up or down.

1. If I up-vote a posting that already has like $250 the reward payout increases for that post.
2. If I up-vote a posting that has a small reward like $9 the reward payout decreases for that post.

At first I thought my voting power dropping below 33% was causing the negative behavior. I've been trying to keep my voting power above 40%... but, it's still happening. Any ideas on what could cause this? Should I wait until I get my voting power back up to 70% or 80%??

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You can see here my voting power is almost back up to 50%.
https://steemd.com/@michaelmatthews

Any info on this subject would be helpful... thx.

I really want to understand this stuff.

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Sincerely,

Michael Matthews
^{Follow me on Twitter}