FYI, this is the link that explains terrain effects on combat:
http://www.ageod.net/agewiki/Terrain_Effects_on_Combat
This also links to the AGEOD excel spreadsheet link page:
http://www.ageod-forum.com/showthread.php?5358-Official-Files-for-modding
With the specific link listed for "CW2 Database", wherein is located the CW2_DB_Terrains1d file.
This excel spreadsheet contains the MinorR, MajorR and Beach files to which Cardinal Ape refers.
If I understand this correctly, from the Minor River sheet, the frontage is about half what one would expect on open terrain under good weather. The attacker gets a (x 0.75) offensive fire modifier and the defender a (x 1.2) modifier during the first round and so on.
I'm the 51st shade of gray. Eat, pray, Charge!