Seeking Arrow

[Ornedan]

Under what conditions will a Seeking Arrow spell not hit if a hostile commander is in the target province at the start of a turn? The spell description seems to imply that defense or parry doesn't apply, but am I wrong there?

Context: EA Vanheim had raided my province with Vanjarl + some Mounted Hirdmen. On the next turn, I cast 2 Seeking Arrows at that province, but neither hit the commander.