Modicon Remote IO Drops

I am trying to setup remote IO drops. I have found the problem, but just trying to understand why it happens the way it does.

Situation 1:
Using the Quantum 534/434
with the MA-0185-100 tap with 14dB loss
to the J890 - comms failure

Situation 2:
Using the Quantum 534/434
with the MA-0185-100 tap with 14dB loss
to the P890 - connects successfully

Situation 3:
Using the Quantum 534/434
direct connection to
the P890 - connects successfully

Situation 4:
Using the Quantum 534/434
with MA-0185-000 at 10dB loss
the J890 - connects successfully

I am hoping to use the J890 instead of the P890 and wonder if only the old taps at 10dB are compatible, as the above tests show. Or am I missing out on something which should enable the use of the MA-0185 taps?