Stephen, re your second point - apologies there shouldn't have been a reference to flare in the second scenario. I had originally also typed up a third scenario in which a wedge was photographed in various ways (which I abandoned as I don't like those methods) and I must have screwed up copying/pasting sub-bullets along the way. Too late to edit it unfortunately.
Regarding the formula, I have to think about that some more. I didn't think that formula could be used on it's own for what I was trying to figure out. Thought it would be more involved.