Better to do an analysis for the given airframe/engine combination. I would be expecting to see an initial descent with some power, then a FI descent for the lower levels ..
I would agree.
It should also be remembered that on some engine designs, idle descents are to be absolutely avoided, the RR Dart is a classic example.
It is also interesting to note that on some jet transports, complete idle descents are
not the most economical, contrary to popular belief.