When you use a rectangular region to determine if an ROI fits in the FOV, then this registry entry defines the percentage of the FOV to use. This registry entry is used in auto shutter mode or when the "VisionDCCFOVSplitSafeMode" value is set to FALSE.
Entry Name: VisionASFOVSplitWHPercent
Entry Type: Whole Number to specify percent. The default value is 95.