Robot Carnival is a 1987 OVA (also released in theatres) composed of several shorts of varied aesthetics featuring some of the most detailed and smooth animation ever created.
Bluray :
The 2018 remastered Bluray is presented in 1.85:1 format, letterboxed on a 16:9 display.
In this screenshot from "Presence" (by Yasuomi UMETSU), the closeup seems a bit too extreme :
Japanese Trailer :
The original japanese trailer (a bluray bonus) reveals that Robot Carnival was originally produced for the 4:3 video format and then cropped vertically for widescreen theatrical release.
Here we can see the full frame of the same shot :
Production documents :
The layouts and key animation drawings (found online or in the extras) were apparently drawn in a 1.37:1 rectangle (the standard aspect ratio for 35mm film), but with thin lines delimiting the 1.85:1 ratio within the frame.
The original storyboards themselves seem to have been drawn with the widescreen ratio in mind.
Conclusion :
Robot Carnival is originally a non-widescreen OVA, probably produced in the standard 1.37:1 aspect ratio and released in 4:3 on video.
It has also been released as a widescreen 1.85:1 movie, cropped vertically (except for "Cloud" which was kept full frame). The bluray version is a remaster of an american widescreen copy of the film.
The short documentary on the bluray states that "according to Kazufumi Nomura (the producer), widescreen is the prefered format for the film".
On the contrary, I think the full untrimmed frame should be the preferred format to fully appreciate the unmatched quality of animation of these painstakingly well-crafted shorts.
Here's a few comparison screenshots :
