I don't know why it happens, but it does,, Ive seen it for years,, no dar then meet 10k cons,,
One time I was fighting a single pony,,over and over we would merge from opposite bases,, he would never show a dar till he was within sight, then he was at 10 k roughly almost every time!
I have logged on to see dar that then disappeared, I've upped for an NOE bomb raid only to find many cons at high alt and no dar till they are within VFR..
as for Strats like HQTRs they should have their own RDR