I would thought that, generally, you fire all your pre planned artillery, mortar and SFMG concentrations into the smoke. Same as if the attack came in at night.
However, not much of a game if you are playing the defender in the front line against a well prepared assault, be it 1916, 1945 or 1983. More fun being the brigade/div commander with some reserves to commit.
"Mistakes in the initial deployment cannot be rectified" - Helmuth von Moltke