Now the question here is how is this defined.
again the rules have
A defending unit will not receive Field Works protection and may not ignore a flag when the enemy unit is not attacking across a hex side with the Field Works (normally this is from a hex directly to the side or behind the Field Works hex sides).
So the implication for ranged fire is that Line of Sight (LOS) is relevant. Where the LOS runs down a hexside, and the hexside meets the ending vertex of a fieldwork, does the unit behind the Fieldwork get a benefit?
So in the example;
Example C is clearly not through a Fieldwork hexside
Example A is the case in point, where LOS runs along the hexside, and LOS is not blocked on either side. The interpretation I question is that because LOS could be traced on the 'other' side, the Fieldworks provide no benefit to the defender.
Example B is the case where one side of the LOS is blocked, and therefore LOS must cross the Fieldworks. I presume that the defender MUST get the benefit of the fieldworks here.
I see that Example A and Example B are similar, and should be treated equivalently, but that isn't a universal view.
The only time in any C&C game I can see this example is BattleCry, which give some examples, but these are much wider in coverage, though worth noting the hex at 2 range directly down the hexside is considered inside the 'front' of a 2 hex fence.
Probably something that needs a Borg clarification, unless there is universal consensus I'm wrong. I note that this would apply equally to Ramparts in C&C Ancients
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