In OpenStudio I have varied the slat angle in the material definition for blinds from almost completely closed to nearly horizontal but the Radiance results are almost identical. Looking at the annual illumination map, the hot spots and levels look the same and if I do some overall statistics they are very very close.
I would've expected the nearly horizontal case to have light bouncing off the top surface of the blinds, then to the ceiling, then back down, but that doesn't seem to be the case.
I also would've expected the nearly closed case to not have any hot spots but the hot spots look the same as the horizontal slat angle case.
