Funkarter wrote on May 25^th, 2020 at 8:16am:

the throttle mode is also appears to be incorrect as it indicates Idle not THR HLD, which should allow the flight crew to manually adjust the throttle.

I agree, since the CS 757 manual states the following for the DES NOW function:
"Once the descent is established the autothrottle mode changes to THR HLD to allow the pilot to adjust the rate of descent with power changes."

The cruise descent version reads "Thrust levers can be manually positioned to adjust the descent rate", suggesting that indeed THR HLD would be the correct FMA for this flight phase.


I also found a 777 FCOM online which described FMA behaviour:
---
"An early descent is any descent initiated prior to the T/D point. There are two
types of descents that occur prior to T/D: a “Cruise Descent,” and a “Descend
Now.”
Both descents are identical in terms of initial descent parameters; they differ
only in their effect on the existing descent path. The initial parameters are:
· Rate of descent: approx 1,250 fpm
· Autothrottles: initially THR until approx 1,250 fpm, then HOLD
(allowing the pilot to adjust the rate of descent as necessary)
---

If the procedure is similar for the 757, then perhaps the thrust mode is EPR until ~1250fpm descent is established, then THR HOLD beyond that.