Now that my Bloom Sky is back on a wood stand near ground level (about 4 ft above gnd) where I can get to it, I rotated the stem again (leaving the solar panel pointed south) to the point more towards the west this time. For now (no leaves yet) that gives me the least amount of nearby homes and the most sky coverage. Most of our weather comes in from the west too.
The rectangular image is a little hard to think about while pointing the camera. There is quite bit of a spherical equivalent of a full sky image missing on all four edges.
I agree about the UV, not only is not clear what the UV numbers mean anyway, but pointing the sensor with respect to direct sun exposure must have some effect on the readings. I guess for now they are just wide angle relative numbers without much other context.