Following discussions on Discord, as recommended, I am creating a post here for the record.
Currently, when the engine is at Idle N1 and you request the engine shutdown, the Simvar N1 behaviour from Idle to Off is hard coded and far too fast. There is no way we can manipulate this behaviour.
Since our aircraft (PMDG 737) engine sounds are linked to Simvar N1, during shutdown, all the engine sounds fade away far too quickly. This is particularly noticeable in the outside views.
In SU9 you fixed this same issue for the Off > Idle startup sequence, and we successfully fixed the startup N1 performance for our aircraft. It works great.
Please can you make the same type of fix to the shutdown sequence, so we can manipulate the time it takes for Simvar N1 to be much longer in duration from Idle to Off.