Its good that you are thinking about these specific and different circumstances. There is rarely one right answer. However, there are agreed upon accepted official standards, both national and international, about how measurements should be carried out, including the specific measurement techniques, calibration, and uncertainty analysis. As someone who teaches metrology, what caught my eye in your OP was questioning why official air temperature is measured in shade(whether it's at a height of 5, 8, or 10 meters is less important). That's what I was focused on. Hopefully you understand that now. Keep up the good work. Always dig deeper for a more profound understanding. There are specific situations that call for some deviation from accepted norms. The context is important.