Perhaps if you described the use of this kit as when it was fitted to HC2 Chinooks others with an aviation background could judge for themselves whether it plausibly explained their actions - perhaps the penny would drop for you yourselves.
As I have said often before, you don't have to get hung up on the issue of this particular equipment - it is just my suggestion as a candidate for what could have had them approach the area confidently, and which could have misled them if misused.
What the evidence strongly suggests is that the approach to the Mull was an excursion with the intent to return to the clear run up the straight coast of Islay/Jura - specifically, approaching a known LZ.