Defensive Fire ?

[ComradeP]

When trying to hide units, keep in mind that spotting is calculated using the relevant values during the next enemy turn, not the current turn. This is important for the second player, as an increase in visibility on the next turn might mean your units are not hidden.

You also can't hide units behind enemy smoke for the same reason: it disappears at the LOS check of the enemy's turn, even though your units seem to be concealed on your turn.