Well after "some" time I had the opportunity to investigate little further, I found the note:
1773537 - FAQ: TM: Texts for CRM business partners on Web UI
So there's no text determination procedure for BPs by standard, the only solution is enhance/modify the standard source, to be honest I don't think the effort really worth it for my customer scenario, but just to give you an idea, check the hardcoded "DEFAULT" in the Class CL_BUPA_IL_NOTES and think about replacing those hardocded "DEFAULT" by the BP Role ID, of course you must have the Account lifcycle activated otherwise one partner can have more than one BP role and all this stuff won't work, nice uh? 
I hope it helps.
Cheers!
Luis
