I could see that coming!!!
Just like when your flying a H300 you can tell the correct RRPM "by ear" - same with the C20b N1 speed, My H500 had a sluggish N1 gauge and although the N1 "sounded" ready to rock the N1 gauge would drag (always 1st flight of the day) soon realised when, at lightoff the TOT was normal even with the apparent 12% N1.
It was the Gauge!!!. Whilst cranking I found a magic tap tap with digit brings the needle to the magic 15%
A good example of how clockwork systems and lateral thinking by the pilot allow flexibility and reduced down time on machines. Fadec would have got stroppy and spat the dummy. Not good when you are in a remote area!! (been there done that!!)