What I do know is that if the engines aren't chopped by the time the Nr gets down to 60%, they will re-engage
No, as HC and others said earlier, if you have wound off the throttles to idle you are now N1 governed and the N2 is simply a function of the residual thrust. The engines will not respond in that governed range, and that's true of any aircraft - FADEC or otherwise.
(if you don't believe it, try sitting on the pad with the engines at idle and then raise the collective - the Nr will decay with no engine response)