Ah yes, didn't realize they stopped after turn 2. So Really I don't have much of an issue with them. I suppose if they really need a big fix, perhaps until the end of turn 2, on a successful Ld check, a ship can fire at a Mimic ship but with a further right shift on the gunnery table, in addition to the one already given by shadowfields. After turn 2 they cease to function as normal. Maybe even give them a Ld penalty if they are a certain distance away. If they fail they can't fire at that target, and may choose another target as normal.
Also another question I had regarding Shadowfields (and Holofields). Do you get the right shift for gunnery while within 15. It says it offers no protection of any kind, but it is stated after the rules for the save you get. Just something my group was wondering.