OK. I just skimmed the article by @azircoin. The very simplified take home.
KE = Author Rewards + Curation Rewards/Held HP
KE = 1.0, you hold exactly as you earn (approximately!)
KE > 1.0, you hold less than you earn
KE < 1.0, you hold more than you earn
Read the analysis and reasoning here:
https://peakd.com/hive-13323/@azircon/top-1000-hive-stakeholders-moments-of-pleasure-years-of-pain
I'm sure it takes account after you claim your rewards. Also I think if you earn half HBD half HP, only the HP will be taken into account.