Krishna
I recentered the c-BRS based on a visual inspection of the instrument. The two interferometer arm-lengths were mismatched on the order of ~1 mm and were accordingly adjusted. The differential tilt signal may show some improvement, assuming it is not limited by other noise.
I have also been investigating the excess low-frequency signals in c-BRS by comparing it to a host of nearby sensors. So far, the likely suspect appears to be air pressure, though I don't yet understand the mechanism for the effect. I'll fill in more details tomorrow.