I mean, it’s their choice to make. If the party wants to try to catch the approaching creatures off guard, they absolutely can. They just run the risk of the creatures not being hostile. Again, seems like a shame to throw away such a decision point in favor of having ambushing them be the obviously right answer.Which in all three cases has the party voluntarily cede any chance of catching the foes off guard and getting in that sometimes-highly-important first round of shots and spells. That don't sound much like a winning idea in the long run.