This oddity happened in a recent game.
A unit of Babylonian heavy chariots (four bases wide) charged into contact with a three base frontage of Sumerian heavy chariots and its neighbour unit of infantry.
The Babylonian chariots have the shock cavalry rule against infantry only. In this probably atypical situation do they benefit from the shock cavalry rule against both units ? just against the infantry ? or do they not use it at all through not going full-speed into the chariots ?