Some clarifications regarding my previous statements:
Anime studios typically work in paper, therefore the pipeline is catered to paper specifically. The 2340x1655px number is actually the typical scan resolution for paper sakuga at 200dpi. Each studio has their own inhouse template for digital use, but because each cut would be printed out, checked, and scanned back in, the resolution of the template actually doesn’t matter as long as its consistent (this is also why studios will supply you with their own template). I haven’t worked in anime for very long so I don’t know what a completely digital studio would use for their resolution.
The issue with re-scaling the entire canvas is the following: when downsizing, the lines and details became inconsistent with other cuts using default resolutions, compositors also don’t know how to composite the scene because the resolution became different from what they are expecting (imagine if every other cut is in 1920x1080 and suddenly one cut is 3840x2160), and its something that can cause confusion to the next person handling your cut (in the case of working professionally).
You really don’t have to worry too much about extremely small details, its not something people necessarily notice. I’ve only personally see 150-200% up-scaling being used on crowd drawings and very faraway characters, unless the faces became too meguca, its generally advised not to abuse up-scaling. Sometimes there are instructions in the settei on how to simplify details when it became too small, but in general its up to the animators.
Talking about different size paper (20f to 260f)… As far as I know, I’ve never seen non-standard size paper being used for production, people typically tape two or more pieces of paper together if they need to draw larger (although there are nothing stopping them from using larger paper, I reckon its not a common practice).
In practical usage, 20f to 260f refer mostly to the scaling of the camera frame. Because the size of the pegholes (tap) must be consistent for the sake of alignment, and the pegholes are within the template, the size of the template has to always be 100f regardless of the size of the camera and the drawing space
^ You can take the above layout as an example of what I’m trying to say.
Camerawork is very sensitive, so there are templates on what the camera frame would look like from 20f to 150f and onward. Which is why sometimes you see charts like these.