https://hive.blog/steem/@steemitblog/hf21-sps-and-eip-explained
basically the big change in that hardfork went from linear rewards to a curve that has a penalty the lower the votes are on a post and the penalty ends somewhere at 20 hive in rewards, meaning that spam farming won't be able to hide with a lot of small votes leeching as the smaller they are the more they are penalized but at the same time it made smaller accounts vote's less effective unless they vote on posts that also receive votes from other stakeholders.
At the same time curation and author rewards were changed from 25/75 to 50/50 and the 25% "free downvote" pool was added. This was meant as a package with the curve mentioned above that all 3 in combination would make for better content discovery and distribution and less farming/self-voting, etc.
Thank you for your explanation... I needed this basic idea, I was not so sure...