Ok guys, instead of hypothesizing just look @ the code. First, refresher on what it does is here https://springrts.com/wiki/Gamedev:WeaponDefs
There are 2 targeting shapes: cylinder and sphere. Then there is ballistic traj. No strange ellipsoids=)
Now to the units: Glaive range is actually NOT cylindrical. Ripper range is not cylindrical, neither is e.g. Mace. In fact vast majority of non-AA units do not have this flag set.
Here is the full list of units with cyl range that are not dedicated AA:
dronefighter.lua: cylinderTargeting = 1 - who cares about com drones
dronelight.lua: cylinderTargeting = 1 - who cares about com drones
gunshipheavytrans.lua: cylinderTargeting = 1 - no problems there AFAIK
planefighter.lua: cylinderTargeting = 6 -- arguably also AA case
planeheavyfighter.lua: cylinderTargeting = 1 -- arguably also AA case
shipscout.lua: cylinderTargeting = 1 - this gives it AA capability, quite OK imo
striderdetriment.lua: cylinderTargeting = 1 - who cares
amphimpulse.lua: cylinderTargeting = 1 - ARCHER
shipassault.lua: cylinderTargeting = 5.0 - huh? (that is on main weapon btw)
So, as I pointed out, Archer having cylinderTargeting set just like siren, and practically no other unit, points out that the idea was for them to be able to hit e.g. ducks that are like VERY DEEP. Whether it is actually a good idea or not... I'm quite certain that being able to hit air is a negative side-effect.
My suggestion would be to mark units for not targeting airplanes at all. IMO that would be easiest and most reasonable. Second best would be to give them spherical range like all other riots and slightly better range to compensate for depth.