Like I said before, the combined fire rule as written contradicts the principle concept of TOI with regard to a limit of actions per player. It completely destroys the balance and makes the game frustrating to play. That is why I limit the no. of units that can be in combined fire attack to that number of actions allowed per turn by the scenario. Just doing that, still allows a player to fire as many as 9 units with 3 actions, before the opposing player can fire. So often, I will use a rule that all units that participate in a combined attack expend one action per unit. Then the Combined fire tactic will be more realistic, and used only when it is neccessary to give a better probability of taking out a difficult target like a Tiger or King Tiger. It would allow the defending player a chance to move the unit away, if it survives the attack, because it will be his turn right after the attack, since the attacking player had to expend all his actions at once.
Limiting combined fire rule allows the defending units in a hex surrounded by enemy units a better chance to hold on, and allows for more scenarios where defender is outnumbered, but by using tactics can delay and hold out long enough to get reinforcements or win the scenario. This could work even better if spotting rules (in addition to camoflage)were added, so that units in woods, bldgs and hedgerows are not auto spotted just by having a line of sight unobstructed to the hex. It compensates somewhat for the inevitable "perfect" intelligence aspect of TOi, and would allow both players to set up units at the start ,in line of sight of one another, since they would not be spotted in woods/bldgs they are in, until they moved or fired. or there was an enemy unit that moved next to them.