The high frequency noise is same for old and new beam spots, but is increased for 50Hz detuning compared with the one on resonance. This noise difference could be explained by the cavity pole effect. The cavity pole effect for 50Hz detuning (half detune) is smaller than the one on resonance by a factor of ~sqrt(2). Please check P.50 of LIGO-T1800447 for the cavity pole effect of detuned cavity.