Distances between two tokens in FGU are found by looking at the closest square of a grid centered around the token based upon the creature size to the target and then "backing up" half a square (and vice versa). For a 5' grid, between two adjacent medium tokens, the two squares will be touching, so bringing each back 2.5', you get a distance of 5'. If there are two squares between a medium and a huge token is 10' for the empty squares and 2.5' for each of the tokens, for 15'.
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If that huge creatures is emanating an aura of 5', it's going to be emanating 2.5' from every outer square, which would include all adjacent targets, regardless of size. If you started from the middle of the creature, a 5' aura wouldn't affect any creature, which I don't think is what you'd want. Otherwise, a huge creature with a 5' reach would also never be able to make a melee attack against an adjacent creature. Unless I'm missing what the discussion is about...
If you really want a distance from the center of a token and not half a square from the edge, you can pass in the coordinates of the center of the token and not the token itself (I think). In regards to the comment about token height a few posts back - I've confirmed that it matches the calculations of raw FGU in 2 dimensions (of course extending to 3 dimensions if one has a height). If you think it doesn't match the raw calculations, I'd ask that you post the differences on that thread and not imply it's messing you up on this thread.