Interesting. In a recent game Cav Armies were slicing Muskets like hot knives through butter but when attacking underlying Pikes in the same city they'd invariably go down to yellow or redline before winning. Likewise with a Cav Army going against a Numidian Merc on a Mountain (strength of 9 vs def of 6 respectively) the same thing happened; in this case the Army got down to one hitpoint before finishing it off. Didn't have the same problem with individual Cav units going against Pikes. Curious, no?
I checked Richie's profile and he was last seen Dec 4, 2013. Reviving old threads is fine in my book, and I've done so several times myself. But, I have a feeling you might be talking to a ghost.