Ford 2011 Edge Owner's Manual page 278

Driving
The CTA system detects vehicles approaching up to 45 feet (14 meters)
away. Coverage decreases when vehicles and objects in close proximity
block the CTA sensors (refer to figure for approximate zone coverage
areas [sensor obstructed for vehicle on left]). Backing slowly from
the parking spot in these situations helps to increase the sensor coverage
and effectiveness.
CTA coverage also decreases when parking at shallow angles (refer to
figure for approximate zone coverage areas [sensor obstructed for
vehicle on left]).
278
2011 Edge (edg)
Owners Guide, 1st Printing
USA (fus)