There are already some excellent tank rules posted by András Kopcsik on Boardgame Geek. They incorporate turning, facing and firing arcs for turreted tanks and SPGs. Flank and rear hits are covered by attacking re-rolls, one for a flank and two for rear etc.
Personally, I have no problem with combined fire rules. If there are six units combining to kill one Tiger there is plenty of historical precedent for that. Some of the German armor requires that attention to take down. How many times have we seen three Shermans combine fire and not even scratch the thing? Then, the return fire always seems to get one Sherm to blow, even in a woods hex. The big cats also clean up at range. The best way to deal with them is two tanks at one hex.
I have not seen the Fury scenarios though. I am curious as to why combined fire is such a threat to the game mechanics? There are many scenarios that need some "serious lovin" (playtesting). The first Squad Leader game had heaps of play-testing and even then, some scenarios were nearly impossible to win by one side or another. The original SQLeader had a great point buy system for scenario design though. Tide of Iron really needs this and I mean one that scores wire, mines, pillboxes, even terrain features alongside all the armor and units.
Decks can be point scored but many operation cards will scale an entire force's point value up or down.
5 Shermans firing in perfect unison at the front plate of a Tiger II would do little better than 5 Shermans firing independently one after the other in approximately the same time frame.
It is purely a function of the main gun velocity, shell penetration, vs the slope angle and thickness of armor plate which determines the capabilities of each vehicles main armament.
.The only spot on the Tiger II that the typical Sherman 75 or 76.2mm main gun AP round could penetrate was the rear plate armor. So a couple of Shermans would try to shoot and break the tracks of the Tiger while the remaining Shermans would circle around behind and attempt to get penetrating hits to the engine compartment, hopefully causing fuel explosion and fire.
During that action, however, if the Tiger turret was not jammed, and main gun still operational, all 5 of those Shermans would most likely be hit and a high probability that all 5 are knocked out or heavily damaged. In fact, kill ratios for Tigers vs most other medium Allied tanks was 5:1. With a Tiger Ace, like Wittman, that ratio goes up as high as 17:1. On the Russian front, 10:1 kill ratios were not at all uncommon.
This is not that well reflected in TOI, probably because of game design balance. But it is TOTALLY BS to design an action phase segment representing on average the time it takes for 3 units to engage in combat, and then BREAK that rule completely, creating a time warp option that allows for one sides ENTIRE force to engage before the opposing side can respond. Not only is it illogical in the game design, but it also did not happen in real life engagment either.
My solution for the Combined Fire rule, is to require that each unit which participates with the "Lead" unit must each expend a concentrated fire action, just as they would if they had fired separately at the same target. This fits with the concept of the Action phase limit of no. of units allowed per phase and then alternating to the opposing player. It still allows for an increased Attack value by adding 1/2 AS for each of the participation units, to the full AS of the Lead unit. So 3 Shermans would still have a more potent total Attack die roll of 16 dice, which is a better odds roll than 3 separate 8 dice rolls. It prevents, however, the totally unrealistic notion of a "virtual super gun" far exceeding the Attack value of the 88 Flak gun, the highest Attack value in the game.
Additionally, as it still allows a limited CF, it also allows for a card to be played that gives one player an extra action, without that resulting in another CF attack in the same players action phase. In this case, the extra action just allows for 1 additional unit to participate with the Lead unit, so the resulting CF will be 4 units rather than the typical 3. Not an overkill, but still an improvement, increasing the 16 dice roll to a 20 dice roll.