Well to be honest... while I like things how they are now, being unable to attack diagonally is a questionable use of mathematics - √2 is ~1.4 which rounds down to 1, not 2, so a diagonal attack should be possible with range = 1. Rounding 1.4 up to 2 is not correct.
I have a feeling this problem affects all ranged weapons, the diagonal range seems to be always overcalculated. Ex. attacking 5 tiles diagonally counts as range 8, even if √50 = 7.07.
This is based, I think, on how the original game calculated blast radii, so it's "X-Com mathematics" and I can live with that.