The passive radar on aircraft is supposed to detect active radars at 2x the range of the radar, as per the sensors config reference and wiki.

PassiveRadarSensorComponent - detects vehicles with active radar switched on at twice their active radar's range.
activated radar makes your vehicle detectable by RWR or Passive radars at up to twice the range of your own radar.

However, it appears that in practice, the aircraft are detecting the ground radar at 2x the range at which they are detected by the radar.

e.g. The Nyx Recon has a radar range of 8000m against air targets. However, because of radarTargetSize modifier, aircraft like the Black Wasp, Greyhawk, Sentinel, etc. are detected much closer.

• The Nyx can see the Black Wasp between 5-6km (approx), and the Black Wasp can see the Nyx's signature at over 10km.
• The Nyx can see the Greyhawk at around 3500m (approx), and the greyhawk can't see the Nyx signature until ~6500m.
• Finally, the Sentinel has a tiny radar signature, and consequently can't see the Nyx until it's 2km away.

(all numbers are approximate due to how i was monitoring this)

Obviously this should not be the case, all 3 aircraft should be able to spot the Nyx at 2x8=16km. In the current situation the Sentinel is useless for SEAD, since the AntiRadiationSensor follows the same rules.