The V-Groove Exterior Backup controls where the Blade Plunges into the Matboard (not the Fallout) on the Exterior cuts of the Outside Cut of the V-Groove.
The Exterior Cut is where the Blade Plunges or Retracts from the Matboard (not the Fallout).
If the Exterior Backup on the Outside Cut of the V-Groove is cut Too Long, Decrease the Exterior Backup.
If the Exterior Backup on the Outside Cut of the V-Groove is cut Too Short, Increase the Exterior Backup.
The V-Groove Exterior Backup field is marked with a Green Arrow on the Configuration screen and the Map illustration.
See: V-Groove Exterior Backup Configurations