WHM Backup: Does "Check the Available Disk Space" include the size of the backup file?

I noticed my automatic backups stopped recently, so I checked the backup log and it was complaining about there not being enough room. It said "Available disk space (14326.515625 MB) is too low. Backups will not run. at /usr/local/cpanel/bin/backup line 1277." My "Check the Available Disk Space" setting is at 15 GB, so this matches the error here. However, there is more than 15 GB free on the disk: there's 25. The backup file is just over 10 GB, so it sounds like it's checking what the amount of free space will be including this new backup. I originally assumed the point of this check was to make sure there would be enough room for the backup file, so would it really include it? Is this amount how much should be left free after the backup is done? It might be relevant to note that I move the backup files off the server and it's then deleted from the backup folder.