It's a pretty bad underlying "issue" with the game really. If you're not getting headshots, you're going to be terrible at the game on aliens because it's actually near impossible to easily kill any human that isn't a complete noob without getting them. Unless it's a movement attack like the goon's pounce or the tyrant's charge, anything that isn't a headshot is essentially unrewarded, relatively speaking, since the damages for anything other than a headshot are so ridiculously low.
If you were to solely modify the dretch's attack range, or all of the aliens' attack ranges for that matter, so it was "realistic" for the model, you'd fuck up the game on a tremendous level.