Sorry for the radio silence. I was busy grading a movie (in ACES).
What I mean is that sometimes the highlight "stick to the ceiling". If I have highlights that clipped or very bright ACEScct will sometimes prohibit me from making them "grey".
This will often happen when I have a high contrast situation. Like an interior with windows etc...
When grading in YRGB in Resolve and using LUTs (etc...) you can always go "before" the LUT and use the "HL" function in resolve to "tone down" the highlights and get the available detail back into the bright area. In ACEScct sometimes that is hard to do. It's like it's trying to keep very bright highlights intact.
We had the same problem with the blacks ACEScc before the added the the toe. The blacks would never lift completely.
I hope I'm clear enough. Can anyone from @ACES or @acescentral comment on this. I'd be surious to know if I'm just way off with this assumption. Cause all colorists here at work feel this when grading in ACEScct.