Part of our course on the Lynx OFT was Fighter Evasion and I recall being taken up in the backseat of a Harrier to observe it from the FJ's perspective as they went hunting for helicopters in the Welsh mountains.
As I recall apart from one Lynx that crossed the valley and 'skylined' himself, they were in the main very hard to spot and engage, even in something as agile as a Harrier.
Relatively easy to spot and call the threat from the helicopter though when down that low. I always did wonder though if any FJ's would really bother to try to engage a helicopter in a hostile environment....clearly some do !