This image illustrates what I'm talking about. The upper image is of the ship's theatre (obviously Main Engineering redressed) from "The Conscience Of The King." The second image is of Main Engineering as seen in "The Ultimate Computer." You can see the ceiling detail in both.

I don't give much credence to the ship's theatre design because it was a one time thing. But the ceiling feature is certainly distinct to Main Engineering throughout the entire series.

I don't give much credence to the ship's theatre design because it was a one time thing. But the ceiling feature is certainly distinct to Main Engineering throughout the entire series.