There are three primary scan zones. 1.) The horizontal traffic scan includes oncoming side and rear traffic. 2.) Rear view mirror scan zone. 3.) The instrument scan zone.
For motorcycles, mounting the mirrors high on a tall shield reinforces the zone 1 scan... shorter shields have less advantage. A good rule of thumb is to use zones 2 and 3 as needed and keep as much attention as possible on closing traffic from all directions. Mounting in zone 2 has an advantage by clustering the Quick-Scan close to, but not overlapping, the primary mirrors. Note: Your eye focus/cognition point is only a target about the size of a 50 cent piece at arms length. The eye's focus/cognition point darts from target to targets as it feeds information to the brain. Double cross-checks are very efficient for both zone 1 and 2. A double cross-check goes like this... Your eye targets the Quick-Scan then the main mirror and finally back to the Quick-Scan. Remember this technique is only as good as your mental focus is... you can look at a mirror and not see a dangerous target. Being aware of eye movement and the eyes focus zone can help you develop better driving habits. Remember both Quick-Scans™ and OEM mirror are important safety tools.