What happens without "armor facing"

[Herr Straße Laufer]

From the manual.

Armor Facing – This only applies to Direct Fire vs. armored (i.e., “Hard”) targets. When this Optional Rule is in effect, the Defense Strength used when resolving Direct Fire is based on the facing of the defender relative to the firing unit (the basic Defense Strength is still used when resolving assaults). These values can be found by pressing the F4 Hot Key during the game (displays the Miscellaneous (Platoon) Data File).

Design Note: The standard (i.e. non-optional) defense value of an armored unit represents an overall rating based on the vehicles’ size (height in particular), armor thickness, close-defense weaponry, and the assumption that not all of the vehicles may be facing in the same direction, especially in a defensive stance.

The Campaign Series Optional Rule for Armor Facing introduces individual front, side, and rear defense values for each armored unit. These values are based on the standard defense values and hard status, weighted by the actual armor thickness of the vehicles themselves. Hence, they do not represent armor thickness per se, but rather the influence of individual armor thickness in conjunction with the game’s existing values.

Hope this helps.

RR