If the downvote button is next to the upvote button, then I think it's certain that some of the time (even if it's less than 1% of the time) people will click the wrong button by mistake. I would consider it bad User Interface and Experience design. If the buttons are not at all close to each other, it would be much better.
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Each side of the reward amount was suggested.
That's close enough for people to understand they are related.