[Alneyan]

I think, if I understand correctly, that you *cannot* catch an army if it moves to a hostile province while you move to another hostile province (where they currently are). You would catch them if you moved to the next friendly province where they are headed, or if you jumped on them via magical movement.

At least, I have never seen an army of mine caught by the enemy when they were followed, and I have used fairly big armies in this situation. They have always avoided the pursuers, at least until magical movement came into play.