The '4.5' just indicates that the needle will fall in the middle of the 9mm foot. If you move the needle to the left, the display will show ' 4.4,4.3,4.2....1.0.0.9.0.8...0.0. Similarly, when moving the needle to the right the display shows ' 4.6,4.7,4.8....8.7,8.8,8.9,9.0'
The display doesn't indicate the seam allowance that you are seeing.