Has the analog whitening settings changed on the ETMX optical lever? I've compared a high-frequency spectrum with a measurement I took in February, and there's reported tons more motion above 2 [Hz], when the ISI motion is roughly equivalent if not better at these frequencies (see attached). Looks there's an extra 1:10 analog filter that's not being compensated or something...
Looking at a previous OPLEV spectra that was made in February on ETMX ITMX and ITMY (calibrated in urad/sqrtHz), it looks like the signal amplitude @ 10Hz (on the three of them) was similar to what you have on your red curve (~0.1 nrad/sqrtHz). Maybe the green trace (reference) was taken with a digital compensation filter engaged, but no analog whitenning ?
Refer to ALOG-10267 for the changes in whitening settings on Feb 21st 2014. This accounts for the two orders of magnitude difference you see above 10 Hz.