I talked a bit to Mike at the Facelift, great shot and great visualization for that shot.
While I have a lot less riding on my shots, I think the anxiety of getting it "right" is high all around, and once it starts to happen, you are there for the ride whether or not you got it right.
It is sublime when it is right! and the images in that short are stunning.
Basically, the Moon is effectively at an infinite distance, and has a 0.5º angular diameter...
to get a shot, you have to move the camera back so your subject, Dean's slackline in this case, has a similar angular extent. Easier to calculate this in radians rather than degrees, the Moon is 0.009 radians in diameter... if the slackline were 50' long, it would have that same angular extent as the moon if:
50'/d = 0.009
solve for d:
d=50'/0.009 = 5730' about 1.1 miles
you then setup the azimuth of the Moon at that time to give you the position, from the slackline, you have to be to get the shot... you can get the azimuth from a number of ephemera