This is actually two requests about the aiming system (the aiming ray that is drawn on the battlescape).
'''1 Forgiving mouse pointer'''
It's nearly an accessibility feature!
Currently, you may aim at a target in the open from any zoom level. The aiming ray is recomputed when the mouse pointer (reticule) move from one square's center to another square's center. Incidentally, it's why it's often better to aim from a top down view than from a "first person" view.
As a consequence, it makes a huge difference between an eagle view and a close-up view, if your hand begins to shake (not due to elderliness, only due to excitation), or the mouse happens to slips out of control. A shot is wasted if you were clicking on the mouse button (or not, if the chances to hit are bad...).
Would it be possible to have a "focus effect" on any valid target (dead or alive actors). An attraction effect such as that used by the window managers in GNU/linux is certainly not wanted, because it would prevent from aiming just beyond or beside a valid target (the aiming ray would go straight on the nearby valid target), but a locking effect, that would require, once a valid target is locked on (tooltip displays aiming chances, etc.), the mouse pointer to be moved further away a little so that the current aiming algorithm is restarted. The target would not "attract" the beam, only "glues" it when it touches it.
This would allow for a sure aiming from an eagle, top-down view, and this would forgive somewhat the "hand shaking".
'''2 More accurate aiming'''
Currently, the aiming ray is updated when the mouse pointer jump from a square to another. Sometimes, this is not convenient because you are quite near to the target (thus, the little jumps translate in several degrees as far as the aiming direction is concerned), or there's heavy cover and the aiming is cluttered so much that the aiming system jumps in turn from a valid square to another that's no more convenient.
Would it be possible to have the aiming ray not jumping from the center of the square the mouse pointer is on to the next square's center, but from the square's center to one of the four square's corners? This way, this could cut by 2 or 3 the angular jump when the mouse pointer is moved. As this feature would slow down the aiming when you want to strafe 90° or so to change target, the accurate aiming mode would trigger (and be needed) only in the vicinity of a valid target.
As an illustration (Request #1), the screenshot illustrates how the Shevaar may be hit when the mouse pointer moves between blue squares' centers.
Now, if you aim at other squares, it will not be the same, especially if the target is nearer to the shooter, and the pointer moves in the other direction.