Curation Effects

I've noticed when upvoting (curating) a post that the authors $ reward will decrease rather than increase. I am wondering if anyone else has noticed this phenomenon? Is it related to my voting power? Is it related to the number of votes I cast?

I am equally amazed that sometimes my vote can add a significant amount to a post.

I vote based on the content of the post and I vote very conservatively, usually no more than 5 times per day. I am hesitant to upvote someone if my vote penalizes them financially.

If there is anyone out there that can shed more light on this or refer me to articles already published, it would be greatly appreciated.

steemit.chat user masterinvestor.