Matrix: E-Madi64 card reporting excessive phase boundary errors

As part of our MADI testing we used a RME MADI box. We chose to connect it via coax which worked fine, but discovered that when connecting it via fibre we see a lot of phase boundary errors and it is because the fibre output from the RME is far too high and needs at least 6dB of attenuation to work.
The RME fibre transceivers are AFCT5179DZ which are a max optical output of -8dB some 6dB too high for our MADI card and as result saturate the E-MADI receiver causing excessive phase boundary errors.

If you see excessive phase boundary errors in the EHX event log you might try putting some attenuation between the E-Madi64 card and the external device
Note:  phase boundary errors maybe be caused by other system errors