Snap is set to be on 1 pixel boundaries for the screen templates. You can easily change it to be any value you want and if you save the template will be set to the new value from that point on.

But I do not understand why you can't set a line width of 1.2pt. You certainly should be able to type in 1.2pt into the line width and it should show 1.2pt. Indeed you should be able to enter values to 2 decimal places, e.g. 1.25pt. Or you can enter a width of 1pix or 1mm or any unit and it should accept and set the line width to the correct value. It just shows it in points always - which is the traditional measure of line widths.