I recently started to fly the Fenix A320, before I had flown the FBW and iniBuilds v.2. I noticed that when I started a managed descent to a cleared altitutde before the TOD, which was calculated by the FMS, the Fenix would not engage the DES mode, instead the MCDU drops a message about a new configured CRZ altitude, and the FCU configures V/S -1000ft descent. The FBW and iB v.2 always engages the DES mode immediately.
Which is the “correct” behaviour? And what did I miss, in case the Fenix should have engaged the DES mode?