We've consistently seens PRCL coherence with DARM that is higher than MICH and SRCL, and the coupling doesn't seem to be reduced well by decoupling PRCL from SRCL and MICH (see 77416 and 77289).  Here are some plots based on old LSC injections made when OM2 was cold, on May 9th.  Using the PRCL excitation, I've made an exess power projection to DARM, SRCL and MICH.  Then using the MICH (or SRCL) excitation I've projected where the PRCL contribution to MICH (or SRCL) noise that's from PRCL should be in DARM.  Both are much lower than the PRCL projection to DARM, indicating that this PRCL projection isn't a double counting of MICH and SRCL noise, and confirming that we won't be able to reduce the PRCL to DARM noise by improving the decoupling of PRCL from SRCL and MICH. 

Camilla has taken a more recent set of these injections 78782, so I will try to run this script for those injections.  I'd expect to get a similar result.  Camilla has now taken measurements to implement a PRCL feedforward. 

These measurements and script can be found at /ligo/home/sheila.dwyer/Noise/PRCL/PRCL_projection