When I read through the CRB about vigilance vs. cool, it seems to make walking into an ambush as a straight dice roll for initiative between the cool and vigilance skills. Wouldn't one expect the ambushers to have at least one boost die simply because they know to expect (or are already watching) the approaching target. I can see additional boost dice for camouflage and what have you, but wouldn't the simple act of ambushing someone give you at least one boost die of advantage automatically?
On a somewhat related note to vigilance checks, how would you handle setting up explosive mines? What method would be good to see if the character randomly steps on a mine or simply walks by it unknowingly?