Originally Posted by
AA757
During a descent in managed mode, the thrust is set at Idle + delta on all Airbus A/C, this is to give some margin to the pilots in case the tailwind is stronger than estimated by the FMS, the theoretical descent path is calculated assuming a descent at Idle + delta. As soon as the pilot flies in selected mode, the thrust reduces to idle.
Any FCOM reference?
Not sure if this is the case since I have seen many times thrust really set to IDLE in MANAGED MODE also.