Section 8.4 COMBAT MODIFIERS
"EACH ENEMY FRONT IN BASE CONTACT -1"
"EACH ENEMY FRONT IN BASE CONTACT BEYOND THE FIRST -1."
So if my infantry unit moves into close combat contact with an artillery unit and the two square up in the front. And then an enemy infantry unit moves into contact with my infantry rear edge than my unit fights at a -1. If another enemy unit made contact on a flank edge then my unit would fight at a -2 modifier.