I took a run in LeftHRSBuff, the FB input is indeed taken into account, since the VME ADC blocks the trigger since it is not in the readout. When in the hall I unplugged its busy and I started to take triggers. Looking at cosmics with T5, I still see a TS busy larger than the front end busy at around 30 Hz, so I might not have gottent the Fastbus buffering right.
Figure 1