.....it may have just been one of those occasions where they were in each other's blind spots and simply didn't see each other.
Very probably.
Many years ago, I was pottering along at low level in one of HM's Buccaneers when the Voice From the Back casually said "Have you got that guy, left 11 o' clock?".
"Yes", I replied, seeing an aircraft in the distance, "looks like a Herc, but it's miles away."
"No, it's not a Herc and it's pretty close!"
Then, from behind the canopy arch loomed a Jaguar. It was indeed 'pretty close'. It must have been
exactly in my blind spot.
It happens. Only way to mitigate is to keep your head and eyes moving. All the pretty coloured paint and flashing lights in the world in the world won't help if it's hidden - neither will silly NOTAMs. And no-one will countenance the cost of fitting electric alarms to Das Teutor.
As I wrote earlier, what is different about AEFs, their pilots, aeroplanes, aerodromes and practices of today compared with 10-20 years ago? When the only incidents were usually caused by staff officers taxying Chipmunks into solid objects?