This thread needs to be kept at the top of the forum list until Sam gives a more comprehensive answer.
I think that the problem really stems from the fact that both the original post and Sam's answer are not worded very clearly. We are then struggling to give clear meaning to those imprecise words.
For instance in the original question are we talking about a unit that is touching the wall along its entire length before forming square? Is the subsequent square in full contact with the wall? Is there a gap between the wall and its starting and finishing formation? If so how deep? What if the wall doesn't fully cover the frontage of the two units? If there is a gap between the defender and the wall, are the basic or optional rules being used for movement over obstacles? Does the infantry straddle the wall before or after formation change because the optional obstacle movement rule is in play? - Well you get the idea! There are many variables all with different possible answers that would each be correct in their specific context.
In Sam's reply he says "There is no "vs Cover" penalty for cavalry charging infantry, rather only an "in Bad Terrain" penalty, which doesn't apply here." If this is a statement about the modifiers to the attacking cavalry unit then of course it seems correct.
The cover modifier only applies to the defender not the attacker. The specific 'Inf v Cav +2 for Cover' is a defender bonus.
The bad terrain modifier only applies to a Regular attacker who is in or who is attacking rough terrain. Assuming the wall isn't in a wood then there is no Bad Terrain -2 for the attacker.
Cam
"He was asked if infantry get a cover bonus against cavalry, and said (correctly) there is no cover modifier for infantry v cavalry combat."
So how and when does the +2 for cover that specifically applies to infantry defending against cavalry come into play? Perhaps you meant to say 'cavalry get no cover bonus against infantry". If "there is no cover modifier for infantry v cavalry combat" then what is the section on page 56 there for?