Why doesn't icloud backup size add up?

I partially figured out the problem.

I have an iPhone, iPad, and Macbook that use the same iCloud space. Apparently messages take up iCloud backup space, and there's no way to turn it off unless you delete all the messages.

I deleted all the messages on my Mac, iPad, and iPhone, and I was able to free up 3gb of iCloud space.

Even after deleting my messages, it did not free up the space right away. I had to delete the backups, and backup from fresh. Then the size reflected the changes.

I guess if you send/receive a lot of photo messages and have multiple devices using the same iMessage, you end up wasting iCloud spaces. I could be wrong, but they seemed all backed up separately even though they are the same messages.

Anyways, there's still a mystery. After deleting the messages, iPhone and iPad now only use 800mb together. However, if I go to iCloud on my Mac, it says I have 600mb of documents.

I have almost nothing on my iCloud drive, less than 30MB. Where would this mystery documents be? I also deleted all my messages on my Mac, and photo library is unchecked.

Now, my iPhone uses 600MB, iPad uses 200MB, and the mystery documents use 600MB. The total usage is 1.4GB, and I have 3.6GB free.

Does anyone know where I can locate the mystery documents?

Thanks!

I found the mystery documents when I went to system preference > iCloud on my mac.

Are you sure about messages getting backed up only once? When I deleted messages on iPhone, it did not reduce the backup size for iPad. I had to delete all the messages on iPad too.

The organization of iCloud seems not well thought out.

First, Apple should really informs how much space each app and device is using iCloud space when you go to iCloud screen. Messages should be there as well. Then people can either turn off the message backup or delete in order to free up iCloud space.

Then there are too many places for similar things. For example,

Settings > icloud

Settings > general > storage & iCloud usage

Top of that if you go to Settings > icloud > icloud drive, many of the same apps are listed in there as well. Then there are apps listed under documents when you click manage storage. Also there are apps listed inside indivisual device.

There are two different places where you control how your photos get backed up.

The back up size gets displaced in different places on IOS, and sometimes they are not the same number.

Lastly, if you turn off indivisual apps from the backup dialog on IOS, all the apps get turned back on when you delete the backup and backup from fresh.

I wish Apple made iCloud less confusing!

Thank you for pointing out the difference.

Perhaps Apple should distinguish in the user interface for iCloud backup vs iCloud sync.

If I understand correctly, backup is for individual device, and sync is for an iCloud account for multiple device?

Then would message be a backup since I had to delete twice in order to reduce backup size for both iPad and iPhone?

If photo library is a sync, why would it be inside backup setting for individual device? Maybe photo stream is sync, but not photo library?

The user interface for iCloud, on IOS OSX, and TV Os should be redesigned to make them clearer and simpler. It's very confusing... Very non-apple like.