you know, i dont think Crouching has any effect on the spread of the pellets at all, i was doing a few experiments the other day and it seams the bullet spread is always the same, the only thing that changes is the Center of the spred, depending on the CoF. ( ie if you jump and shoot, the spread will still be tight, but in the top right hand corner of the screen, instaid of the center )
But on the plus side , Ducking does make you somewhat more warpy :P