Splat!! - That was a typo, sorry! I meant the hypotenuse is longer horizontal distance by a factor dependent upon the angle, specifically the multiplicative inverse of the cosine.
Zak, I assume you were asserting that the explanation I disagree with is false? I am actually just using this as a 5-minute work break (00:38 on Sunday morning and this is what I'm doing, ugh), so I don't have time to read that thoroughly at the moment, but plan to as soon as things calm down a bit. However, the diagrams in the website you put up make a bit more sense than the explanation I was operating under - I suspected it had more to do with the relationship of the line of sight through the sights and the bore-line as a result of the incline, which this article appears to suggest. Hopefully I'm looking at it correctly, it's been a long week unfortunately.
Thanks for the discussion, happy for the clarification.