[DRG]

A unit that had "C" applied is as Andy said, an attempt to find cover/concealment and if the enemy stops firing then *maybe* you have broken their LOS to you..... or maybe they are out of "shots" for that turn...or maybe in RL they are taking time to regroup and know exaclty where you are

The unit " in cover" may only have a view of dirt and weeds and since the firing stopped assumed they are out of LOS..... but maybe there is an enemy observer where you never expected one to be who has eyes on you so YOU may think you out not being observed but actually are and that's why pressing C *MAY* have an effect....... or may not and why it's not the same as being "dug in"