Wind speed not same as SIM_WIND_SPD

I’ve set the parameter SIM_WIND_SPD as 10 with SIM_WIND_DIR as 180 degrees. Now when I simulate in SITL( flying the plane in the direction of headwind i.e towards south), the wind speed in values widget of QGC shows 5.1 m/s with direction 123.2 degrees.

Why is this happening?