You very well could be right. It just seems to me that the surface area is large, and the value of exploitation is high. Anything from targeting sensors on the plane with lasers, to exploiting ground stations / satellites / IFF systems, to interdicting component supply chains and inserting remotely triggerable flaws. These are just the things that hit my particular mind immediately, but i'm sure there are many other possibilities.

Keep in mind that military aircraft have tons of specialized systems on them that civillian aircraft do not. And further, that countries would be willing to spend, literally, billions of dollars to build systems that could exploit flaws like this. So even for quite exotic ideas like say, designing ground objects with exotic shapes that have radar signatures that trigger flaws in onboard processing software, or whatever.

I'm just making things up here, but there are undoubtedly teams of physicists, avionics experts and cybersecurity experts tasked with studying this, even if just to ensure our systems are not vulnerable to it. It's possible that all that has come to nothing, but it would not surprise me if it hasn't.

Australia has had over the horizon radar for decades. Maybe there is a 2020+ version that is sufficiently fine grained to use for training to the target.