Thank you @barit1;
Excuse me, I have seen your reply just now.
You implied that there is 2.5% change for each 1% N1. Although you noted that this is for high power region, I extended this relationship to low power regions to find some rough results and I saw the followings;
~94% N1 for 85% thrust as you said
~58% N1 for 30% thrust
and never found a plausible N1 for 7% thrust, which is due the fact of the accuracy of the relationship in low power region. May be another relationship is existed for this regions.
Although we are talking some quadratic or cubic function between net thrust (Fn) and N1 at high power, in (C.E. Otis, Aircraft GasTurbinePowerplant) textbook, the Fg (gross thrust) is linearly related by the N1. Perhaps I get confused between Fg and Fn as expecting a lineer relationship between the N1 and thrust (Fn) as well, for no reason.
Thank you.
If you have comments please feel free.