I'm curious what the per acre rates are you got quoted? $8-$9 p/acre will cover most acres here.
My brother is a cropduster, and my dad did it for 20 years or so. "Here" 5 gallons is the minimum rate, with a lot at 7 gallons, and occasionally 10 gals. A lot of trials have been done here over the years examining water rates for different chemistries. Long story shorter, a blind coverage test determined that 5 gpa actually had better fungicide coverage than 7 gpa. The nozzles on the planes are CP, which use a little different technology theory than ground rig nozzles. If applying phosphites on potatoes however, then the minimum is 7 gpa, anything less and leaf burn occurs. Once in awhile my brother will bring a plane from another region to help out if he gets behind in the summer, first question he asks is if the plane is capable of 7 gpa because most of the Midwest planes max out at 5 gpa, and 5 gpa with phosphites = upset farmer.
Cerone/Ethephon is a great shower of coverage patterns. Anything less than 5gpa shows significant streaking later in maturity. That's the same pattern your fungicide is going on with.
A few years ago a neighbor that has a history of contending with DON split a pivot. 1/2 with plane and 1/2 with ground rig. Plane was 5gpa and ground rig was 20gpa. Upon testing the grain, there was no statistical difference, but the plane side was slightly lower. Should note, the ground rig was NOT using forward/back nozzles.