3a Tiebreaker only applies when a Mine is placed during a Faction Action. It also states what the tiebreaker is on the Faction card. You will notice that each Automa faction has a different tiebreaker.
Then why is tiebreaker 3a of the build mine action stating to consider faction action if applicable? Sounds to me like you also use it for mine building. What did I miss?
Edit: Nevermmind, I realized the player « aid » sheet was misleading. The rules in the automa booklet are clear.