Do searchlights have a ceiling? trying to spot planes at 5000m

[[F.Circus]sith1144]

Hello! I'm working on a coop night bombing mission and in my testing it seems searchlights can't find a test aircraft flying at 5000 meters, but can at 4000. Do they have some kind of soft ceiling? did I set something up wrong? for the purposes of testing I am using a single aircraft in a cloudless sky. Is it possible to get them to find aircraft a little higher? I have tried putting the Engage Aircraft attack area command up in the sky, but that doesnt seem to have made a difference. I have also tried attaching radars.

 

I have attached the mission I am working on.

NightRaidRouen.zip