This post just led me to do some checking on controlled airspace around airports, to look at the size of these regions of controlled airspace, and compare that size to what seems realistically needed to protect manned aircraft from possible collisions with drones. How much space is realistically needed? I don't know how FAA measures it but if we allowed 3 times the max height at which drones are permitted to fly, eg a manned aircraft at 1200 feet, that seems it would suffice to me.
As an example, I looked at San Francisco International Airport,
I noticed from the B4UFLY app, that the controlled airspace around SFO extends 4.5 miles north of the airport. Using the flight app
ADS-B Exchange - track aircraft live I checked the altitude of arriving and departing flights from that airport, and it seems that airplanes are higher than 1200 ft if they are 3.3 miles from the airport. So that in itself suggests that the controlled airspace around SFO is about 1 mile more in diameter than my theory would indicate it needs to be.