Thanks Nick! You bring up a great point about the sketch sheets being biased to the horizontal. Being able to look up and down has been secondary in people’s minds, and the sketch sheets could be a better job of reminding people to think about the vertical possibilities too.
Mike Alger has a great explanation of the comfortable head turning angles in this video (jump to 5:30), and more in his paper Visual Design Methods for Virtual Reality.
I’ll definitely add some thought around the vertical in the next iteration of the sketch sheets!