This has been bugging me since beta. It's not that the click box is unresponsive, there just ISN'T a box. You literally have to click directly on the character/monster. In between the arms or legs doesn't count, the space between the name and the character doesn't count. They need to fix that and make it a square around the character, and add a slight click and drag allowance window, because that's bound to happen when clicking moving targets.

This thread really need some more support, with the current horrible state of tab targeting