I aim for the far side of a group, at the max range of the cone, if I aim at all.
The idea is that if your target is right next to you, they don't have to move far to swing the whole cone away from where you want it to go. By comparison, a target at the edge of the cone has to go farther to mess up your alignment. To illustrate, in the diagram below, we have a 90 degree arc that represents the Eviscerate (Widow_Training) power. You can see how the Red circle can move the arc of your attack more with the same distance traveled as the Green circle.