Well, from the way I understand it, what really matters is the Speaker field.
Taking as an example the original file 22aa_zalb01_01.dlg with Canderus and Juhani as party members we have the following:
E4 - *hmph* Maybe we should have brought the Wookiee out. This place looks... untamed. [sPEAKER: Cand LISTENER: Player]
R3 - (continue)
E5 - Are you afraid of the wild, Mandalore? Are you a coward? [sPEAKER: Juhani LISTENER: Cand]
R4 - (continue)
E6 - Mandalorians are not cowards! We're just practical. [sPEAKER: Cand]
R5 - (continue) [END DIALOGUE]
The problem with this is that line E6 should see Canderus facing Juhani while he instead faces PLAYER, which seems to be the default action. Adding LISTENER: Juhani to E6 does not fix it.
The only thing I could think of to make it work was to add a new empty Entry after R5 and set SPEAKER: Juhani to it. By doing that, Canderus delivers its last line facing Juhani, as it should be.
Is there a better/smarter method?
Cheers!