What a fine idea and a fun experience! I understand the difficulty, however, in getting into a scenario where you have no control of distance, lighting, or position. Kinda like courtroom drawing for me. I do it for the money, however. I would not willingly get involved where there is so much chaos. Courtroom drawing is my absolute worst work, and at the same time, ironically, the highest paying work. (Pastel, of course.)
But when you have to work from such a distance, 20 feet, it is really very difficult. I congratulate you!
I really think you are having a good time drawing! When you get to have some models that are at your control, with your own lighting and at a reasonable distance, you will really appreciate it!