author and curation rewards are "just" number of HIVE on what you received at the given moment, no interest is involved here as far as i know.

For the next point i can only reason by, because i do not know how it was in the past.

At the time you receive the 50%/50% rewards the total earned hive is divided by 2 and one part is converted to HBD the other part is stored in HP.

So when you try to keep track of how much does the HBD represent in HIVE or HP, at the moment of payout it the same but then the price changes of HIVE making the amount of hive received in the past different. That seems to be unwanted behavior so just use the total HIVE you receive from the rewards. 1 HIVE stay always 1 HIVE

Down side, who knows this, how to educate user that are just joined for the game and do not have clue on this topic.

This how i understand it at this point, only diving deeper in this matter since the last two weeks. So disclaimer: i do not have all the knowledge about this, also a learning journey for me 🤣