Regarding Marathon, I said one rank deep seems right, specially with a few miniatures, but as FoG has no scale, when increasing the number of points and miniatures it is no longer possible to depict battles properly. This is the case with Marathon
It most definitely was, from Livy:
"There were 16,000 infantry in the Macedonian fashion. known as the "phalanx." These formed the centre, and their front consisted of ten divisions; between each division stood two elephants. They were thirty-two ranks deep"
Sorry, you were right. I was using a secondary source I should not rely on that much. Anyway, I have read Livy's account of battle and I interpret that it was the spreading of panic of their troops routing what dissordered the phalanx more than the good performance of the legionaries. In FoG terms they failed their CT for seeing friends rooting, they were crossed by fleeing cavalry, etc. I should take a look at the sources for Cynoscephalae, but is seems we have another candidate for a 32 deep phalanx, something that does not exist in FoG, by the way.
Regarding Bagradas, I don't think that is the case:
"But the first ranks of those who were stationed opposite the elephants, pushed back when they encountered them and trodden under foot by the strength of the animals, fell in heaps in the mêlée, while the formation of the main body, owing to the depths of the ranks behind, remained for a time unbroken. 6 At length, however, those in the rear were surrounded on all sides by the cavalry and obliged to face round and fight them, while those who had managed to force a passage through the elephants and collect in the rear of those beasts, encountered the Carthaginian phalanx quite fresh and in good order 7 and were cut to pieces"
Polybius (I, 34)
In Bagradas it was the cavalry surrounding the Romans who won the day and the capacity of the elephants to keep pushing forward instead of turning back into their ranks. Again, it could be succesful or not, but we do know that in some battles generals increased the depth of the formation willing to have more staying power against certain enemies. That was a risky manouver as your flanks increase and you can be surrounded more easily but certainly it is not covered by FoG.