Accoeding to my calculation, the sensitivity cleaning (toward nearer 10^-18 [m/rHz] and remove peaks and bumps) "only" around 100 - 200 Hz can extend the range about a factor of 1.9.
However, peaks around 180Hz are suspension sapphire fibers resonances.
Blue : KAGRA Displacement
Green : Simulated cleanline with better around 100-200Hz
Red: Simulated clean line with worse around 100-200Hz
Violet: 1.4-1.4 BNS Chirp signal projection ( 1/sqrt(5) factor is included )
Updated
It seems that the most important noise hunting should be done for 180~200Hz noise budget to achieve 1Mpc.
One more stupid questions, can we try to increase laser power to 10.0W, then stabilize?