I seem to remember seeing a graph on it way back. I don't remember the exact figures but it goes down from the moment of posting to the 30 minute mark as a percentage. I don't know the exact figures for curation rewards percentage depending on where you vote in the queue. It is a function of when you vote AND the voting power you have (the stake you put in) so it is not a straightforward value.
It doesn't really matter to me that much I just upvote people whenever. Like someone else said it has the side effect of encouraging people to vote on unknown authors if they want good curation rewards. For me the most important priority is encouraging other users and rewarding good posts. If I get rewarded for curation great but I don't care much about it.
You don't care much because you receive some rewards from creating content, if you couldn't make a penny by posting I think you would be really happy to be able to make money curating. ( and that's about the majority of people in this platform)
I personnaly think we should get rid of the bots altogether with some captcha or something