CullAi automatically rates all photos based on AI score to Rating mapping. AI score of a photo is calculated by taking AI score of all faces of people in that photo and how important they are for this photoshoot. AI score of a face is a measure of better lit, sharper face with open eyes.
AI score to Rating mapping can be configured in Preferences -> Automation -> AI Score to Rating mapping. Default mapping is linear and is good starting point, but you can adjust thresholds for each Rating. If you find a lot of discrepancies in Auto Ratings and Ratings you would have given to a photo, try adjusting these thresholds. Lower threshold for a Rating will give that rating to even those photos having lower AI score.
At any point you can reset these mappings to Factory settings by clicking Reset to Factory Mapping.