Ambushing enemy armies

[Frankenbeasley]

Um, if the ambush screen comes up and the army is attacking someone you don't want them to then click the little flag icon to 'withdraw from this battle' rather than beginning the assault. Your army goes back into its ambush position and the other army carries on their way as though nothing has happened. You simply choose not to spring the trap. At least, this is what happens in my game.

ETA: I completely missed the last sentence of the original post, so sorry if this post is unnecessary. I'm talking about the flag on the campaign map battle scroll rather than the withdraw from battle on the battle map controls.