"Drive at the top" is not a documented or guaranteed situation. If you want to check the startup drive, use the "About This Mac" panel in the Apple menu.
Your backups are in the log in Window > Show Log (for manual backups) or, Window > Scheduled Copies (for scheduled copies, select the schedule and click Show Log).
You want to use "Backup - all files" with "Smart Update" in about 99.9% of cases to do a backup.
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--Dave Nanian
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