What Determines the Diameter of a Moon Halo?

[jmvizanko]

So I got to see an amazing Moon Halo the other night. My question is, what is really the diameter of the average location in the halo, where the light is bent by ice crystals? Is it really as easy as doing the trig with the altitude to your average cirrus cloud, the angle above the horizon that the moon is at, and the 44° cone that the halo represents? Or have I fundamentally misunderstood the phenomena?

 

[mfb]

Trigonometry should work.
I don't see the relevance of the result, however. The clouds do not have any structure of that size, and different observers will see rings at different locations (and even different size, with a different altitude).