My objection to combined fire rule, is not that it is possible for one target to be attacked by several units, in the same action phase, but that the basic mechanx of activating a unit, which requires an action/unit to be spent, is suspended and altered by this CF rule. So you get an extremely artificial accelleration of time, that allows for an unlimited number of units to fire, using only one action, when in reality, EACH of those units would have to be activated by a concentrated attack action, to engage an enemy unit, with each one rolling a separate die roll attack to resolve what that particular weapons effect was.
The CF rule should be changed to "Coordinated Attack" and should be not an "action" but a "type" of attack, which still requires one concentrated attack "action" be spent PER each unit which is participating in the Coordinated Fire attack on the same enemy target.
The calculation method for the single die roll attack, of the original CF rule, is simple enough, so IMO that can be kept as is.Requiring each unit to have to expend a concentrated attack action, will result in most cases, to only 3 or 4 units being able to fire together, in one action phase, after which, that active players phase is over, having spent all his actions for that phase.
I think this would go a long way to correct for imbalanced scenarios, as the side with greater numbers of vehicles will not be able to destroy an outnumbered enemy force, in just one action phase, and before the enemy has a chance to react to such an attack.
3 M10 Tank Destroyers, using a Coordinated Attack, would roll a single die roll of 10+5+5=20 dice, and would expend 3 concentrated attack actions to do so.
20 dice is a potent attack die roll, and just enough to consider using up all the actions the active player has, in his action phase, to try to destroy a dangerous enemy target, like the King Tiger. There is, however, still a reasonable chance, that the enemy target might survive the atttack, and thus, in the enemy action phase, could use a fire and move attack, shoot and then move back one hex, out of Line of Sight. This makes the mechanix of combat resolution, more dynamic, and less absolute, and offers more opportunity for the outnumbered defending player, to use fire and move tactic, or delay tactic, without getting obliterated by CF attack in just one action phase.
This suggested modification also works with another suggestion for damage modification for heavy damage, which is allow heavily damaged vehicles to be able to move to any adjacent hex, (except for hexes restricted for vehicles to enter), using an advance action. Thus, a heavy damaged vehicle is not immobilzed, and a sitting duck, but has at least a slight probability of moving again, to capture an objective, or move back, out of line of sight, and survive another turn.