A is a Large (tall) creature armed with a longspear, giving the creature a reach of 20 ft. B, a Small creature that's hovering 5 ft. above the ground, has 10 ft. between him and the the Large (tall) creature. C, a Medium creature that's standing on the ground, has 15 ft. between him and the Large (tall) creature, in line with the Small creature. Imagine this in three dimensions:
Does flying-5-ft.-up Small B grant standing Medium C soft cover from Large (tall) A's longspear melee attacks?
Note: In context, A was an equiceph from Miniatures Handbook 61 (I like obscure monsters—don't judge), B was a PC who had assumed the form of a Small hex dragon from Dragon #343 39, and C was the fast-moving scout. There was a lot of talk at the table, but I think at least part of our (okay, my) confusion stemmed from drawing lines from corners of squares versus drawing lines from corners of cubes. (I know, right?) Even with miniatures and flight cubes (1" numbered blocks used to represent altitude), we were undecided on whether the dragon granted the scout soft cover from the equiceph's longspear attacks. Eventually, we compromised, assessed a −2 penalty on the equiceph's attack roll, and moved on, but I'm curious as to the correct way to assess this situation.