The Interior Backup is where the blade backs up before initially plunging into the fallout on the interior cuts, such as when cutting a French Stair. 

Interior Cuts cut into the fallout, not the matboard. 

Make sure to select the desired Cartridge Tab and then the bevel type you want to edit from the Current Bevel Type dropdown control before making adjustments. Select Front of Mat if it is being cut from the front of the mat.

The Interior Backup is displayed on the Configuration Map as a black arrow. 

Check against the Configuration Map of the Bevel Type you are cutting to determine specifically which cuts are the Interior Backups.

Interior Cuts, such as on French Stairs, cut into the fallout, not the matboard.  

If the interior backup plunges the blade too late, it makes the interior backup too short.

Increase the Interior Backup.

If the interior backup plunges the blade too soon, it makes the interior backup too long.

Decrease the Interior Backup.

For Backups where the blade plunges into the matboard instead of the fallout, see Exterior Backup.