Auto-backup has a specific target from which the backup is taken according to the schedule assigned to such target. When you use a normal backup scheme in your cloud - the target for auto-backups will be a disk of the Virtual Server; for incremental backups - it will be the whole Virtual Server.
Windows-based Virtual Servers support only normal backups. Thus, even if incremental backups are selected for your cloud, the auto-backup target for Windows VS will be its disk.
The auto-backup may be enabled either during the creation of Virtual Server using the required_automatic_backup parameter, or at any time afterwards. If you enable the auto-backup for a Virtual Server or its disk for the first time (i.e. there is no auto-backup schedule for such target) the system will automatically apply the schedule configured in auto-backup presets.
If you enable the auto-backups for a target with assigned schedule - this schedule will remain unchanged.