iCloud gives you some options to choose what apps can use iCloud. Sometimes, you may find your iCloud backup size actually bigger than the data you selected. That is because will backup some data that won't tell you. Some users reported that messages will take a large proportion of iCloud backup even though they banned it in iCloud.
In addition, iCloud backups include system settings you may not have noticed. Then you can use FoneTool to backup your iPhone data, it supports selective backup iPhone data enabling you to choose which file can be backed up.