Oh dear, maybe I have got it all wrong.
I don't fly the aircraft, and I can't recall where I got the information from, but I was under the impression that with the NAI selected to ON
1) The nacelle anti-ice valves open.
2) NAI is displayed in green next to the N1 indications on the primary
EICAS display.
3) The EEC's increase idle as required.
If this is not the case, then what is the point of entering the altitude at which NAI is expected to be used in the descent forecast page, if it has no impact on the descent gradient?