face-based fixtures on compound vs. basic ceiling

[HVAC-Novice]

I noticed this in a space that has compound (2x2) and gypsum (basic) ceiling and i tested that with multiple face-based light fixtures in RCP. 

placing any of my fixtures on the compound ceiling makes the fixture list the ceiling as host and be the correct way (shining downward).  Also the lighting power gets allocated to the space. 

But on the basic ceiling in the very same space, the very same fixtures place upside-don and don't show a host. i can flip the fixture to have the light source and power be accounted tot he space, but still no host shown. 

those are just simple ceilings originated from an oob template. the only difference is one is basic ceiling and the other is compound. 

I saw some posts referring to something being different between those ceiling types. but non shows how to make a basic ceiling host the fixture correctly. One workaround may be to create gypsum ceilings from a compound ceiling. But before doing that I like to understand what is going on and if that has other consequences? Should we just avoid basic ceilings? 

[ToanDN · Accepted solution]

Basic ceilings don't have thickness so there is no geometry for hosting.  Use compound ceilings.

[HVAC-Novice]

I created a compound gypsum ceiling and everything works as expected. 

I can't believe all those years I just manually flipped the fixtures.... 

Since the basic ceilings violate the "model it as it will be built" rule, I wonder what the purpose is? Is that some legacy feature before ceilings got smart?