I measured again MICH and SRCL FF. I could fit a MICH filter that improves the subtraction. SRCL is still work in progres.
The new MICH FF filter is loaded into FM1, it's better so I'll put in in guardian.
There is now almost no coherence with MICH, and with SRCL only at the ~100 Hz jitter peaks. So I think the current LSC FF are good.