Yes, I tried 4 as a parameter, but I think that's just relevant if you're not in Cylinder-mode.
ZapCylinderAltDiff puts the zapper in a different mode that ist described as above
"... for zapping is the nearest aircraft to the airborne user which is within the upright cylinder of radius ZapAirRang"
To me that sounds like the radius of the cylinder (not a cone) is set by the ZapAirRange value and the height of the cylinder ist the ZapCylinderAltDiff value, with the user in the center of that cylinder.... To my understanding the closest AI within that cylinder should vanish.
For me, that's not working.
EDIT: Even without cylinder mode, diving directly at the ground traffic, I can "shoot" as much as I want, I can't zap the traffic on the ground while I'm in the air. When I land, it works.