Cavalry and Infantry going into assault

[J6A]

I don't know that the rule anticipates a cavalry charge. Normally, a leader would activate adjacent units and essentially tell the guys in the hex to join in, especially if he joins the fray himself. It seems odd that guys 400m away would get the word.

Otoh, I'm not sure that's correct, which is why I asked. Certainly taking the conservative approach can't be questioned by my annoying opponent (i.e., me).