setting the focus box size.

I think I found a cool and quick way to do this.

Press and hold the Multi-function button (Fn2) and rotate the rear dial to select the magnify function then press Fn2 once more, you get a persistent green focus box that is about half the size of the normal focus brackets. It seems far more selective than the normal brackets. Furthermore, this box can be moved around live using the direction arrow keys, in fine increments.