In your example, you are correct in saying he is out of range. However, because of pre-measurement now, the shots he declared are not wasted. He can measure, see that he is out of range, measure distance to something else, and then fire. If he declares he is in range and in fact forgets about Nightshields, if you just remind him, he will be able to select a different target.
Depending on the circumstance, he may want to change the movement of the squad/ vehicle that wants to fire at you because they forgot about the -6'' to their range. Then it would be up to you about allowing them to re-move their unit to allow it to shoot at something else.