I am also curious about how to distribute GCPs, and how many to include, in corridor mapping after looking at the referenced support articles.
My corridor is 3 miles (5km) by 200 feet (60 meters).
I also saw that someone got an answer of having 3 GCPs/per flight (https://community.pix4d.com/t/4950-How-many-GCP-s-#gsc.tab=0). I am curious if that only pertains to varied terrain or should be utilized in all cases?