Question regarding upvote values or amounts

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Hi all,
I have found most of my answers on steemit or by googling, but I can't find anything about the upvoting amounts, or more specifically why some people I vote for get something while others get nothing. I'm not sure I'm explaining this correctly but an example is:
I reply to four posts because I find them interesting, I reply, follow then upvote, but some don't get anything while others get between 0.01 and 0.03

I keep everything the same, reply, follow, upvote, out of four people I did this to, the 1st one got nothing, the 2nd one got 0.01 the 3rd got nothing and the 4th got 0.03. Can someone explain to me why this happens, is it just a glitch or does it depend on the person I am replying too, or something else that I'm missing.

Question regarding upvote values or amounts | Ecency