Running the Reports from Report manager
NTFS | Folders
General Folder Information
General Folder Information by Folder Depth
The Size reported doesn't account for the Sub folders
Due to how Enterprise Reporter calculate folder and file information in the reports, Enterprise Reporter can only calculate the size of a folder by the items in that folder specifically, not within the sub-folders. This is different than you see in windows where it traverses the tree and gives a total size for all items in the folder and all sub-folders.
Enhancement Request TF00001837 has been specified for this and the product team will look to include this in future versions of Enterprise Reporter.