Blind in this position is aligned with the direction of the beam normal solar radiation.
Most of the solar radiation is passing through the glass window into the room causing the SHGC reached the maximum value at this slat position.
When the solar vertical profile angle is further increased in the negative value, the value of the SHGC is decreasing resulted from the blockage of the blind from the solar radiation.
The value of the SHGC is reduced to 0 at solar vertical profile angle of -90 degree.
The reduction of the SHGC resulted from installing the blind behind the glass window is obvious when the blind is in the position that the solar vertical profile angle has positive value.