Exercise 36 is a useful exercise and has created a useful reference chart for the effects of a single diffused light.
Beyond the obvious effects of moving the light fore and aft and up and down the most interesting differences have occurred with the colour of the subject. It shows that the most saturated colour occurs with the light just left of the camera and at the same level as the subject, at 45 degrees to the subject and 45 degrees above and when the light is above the camera so more than 45 degrees above the horizontal.
Above the subject reduces the texture and gives a flat light.
45 degrees above the subject strengthens the colours.
45 and 90 degrees gives the most depth but by comparing fig. 4 and fig. 5 it can be seen that there is much greater colour strength when the light is higher as it is in fig. 4.
Theoretically there should be more form and shape at 135 degrees and this might be try if the subject was also being lit by a fill light from 135 degrees right but the deep shadow reduces the sense of depth.