captain to family member

anyone have any idea what is required to get one of these babies adopted into a family?
I have only had it happen twice since I bought the game when it first came out, and the most recent I had a captain fight a battle once and he became the "man of the hour" even though the battle was easy.

but today I was trying for it with the Carthiginians (sp?). I had a captain win 4 battles, one against a scipii family member, and then take the roman city located on Sicily. I mean the guy took on battle after battle and only lost about 10 guys in total, this set on medium unit scale and against the romans is pretty good. (I used my mercenary missile cavalry and slingers to kill the guys until they routed and then killed them as they ran). Doesnt this guy deserve adoption? he kicked major roman bum and eventually took over all of sicily for me!

this thread has some answers ~:)

https://forums.totalwar.org/vb/showthread.php?t=41124

The speculation in that thread seemed to revolve around what happens in the battle. IME, the actual events in the battle are irrelevant. The trigger seems to be having more provinces than family members. The game appears to use adoption as a way to buff up a faction that may be in danger of dying out due to low number of births or the sudden loss of multiple family members.

As an example, I was playing with the Scipii. Right from the start, I left my faction leader in my capital and shipped everything else to sicily to get some punic punishment underway. Things went well, and soon I was the master of the island. I then moved all remaining family members back to messana, for retraining and to connect with my fleet. BOOM. Etna explodes killing off my entire family save for the faction leader and the little ones. ~:mecry:

But in the next four battles, I got myself a new "son" each and every time. Even the one where captain Lucius and a full stack of romans (on huge US) beat up 300 rebel peasants! Twenty years later, there wasn't any actual scipio's in the scipii family, but the game went on.