Thank you for the quick reply @Sic. Camp Radius was my first suspicion as well. But, isn't the max value for that field 100? If I try and enter a value larger than 100, it auto-resets to 100. Additionally, if I look at the map as combat begins, the mob is well within the red circle. Here's a screenshot:
Immediately after taking this screenshot, I tapped auto-attack and he jumped into action. Notice that the distance to the mob in the screenshot is 21.24. As I mentioned, toying with it manually a bit by tapping forward a little, the monk will jump into action is the distance becomes less than about 20 units...despite the fact that the camp radius is set to 100.
Kak