That is because large staked accounts voted on the posts fairly early
How is this changing the % allocated to curators? I have been through dozens of posts and they all show the same curation reward % which is about 3%, are the numbers displayed incorrect or not?
Not all. I just scrolled through my recent curation rewards for the bigger ones and this one has a good ratio towards curators: https://steemit.com/science/@redalex/german-scientists-have-developed-an-effective-method-of-absorption-of-carbon-dioxide-from-the-air
It changes the % allocated because curation reward is dependent on stake. If a good amount of stake donates curation rewards with votes before 30 minutes, it means more curation rewards in total will be donated to the post author.