potential successor hasn't worked a single time

[Shlazaor]

The heir has always become the eldest son of my FL. Is the successor only relevant if the FL has no living children?

[Shoebopp]

Unfortunately so. First priority goes to the FH's sons, then the FL's. Only after those two lines of succession are out of the picture does the potential successor become FH, and even then it might not be 100%. The potential successor trait gives a hidden boost to Authority, a stat that all FMs have. It's possible for a non-potential successor to have high hidden Authority because you've won too many battles with him. As a result he'll become the FH

[blackbirdgriffin]

As shoebopp it's indeed about authority and the ancillary is only an added buff to authority, in my experience I've always had a success because once I identify the 3rd in line he becomes my principal general so that his authority improves just as you would for a faction leader with low authority.

For anyone more knowledgable out there is influence a factor in the calculus of authorority or is it just battles?