[Rules] Fog of War modifier

[Poor Yorek]

I remember a +1 modifier to Fog of War checks in activation segments when a player chose to pass. I seem to be having trouble finding the reference to the rule. Does anyone else remember something like that? Where is it found?

I suspect that you are thinking of Battle of the Bulge.  To cite:

"If a player passes, modify his or her result (on 3d6) by +2.  Modify the die roll by +1 if a night turn (visibility is 1 hex)."

I checked also vs. Eastern Front & Beyond Normandy, two other older games, and they do not included the "pass" sentence. 

Ah, Afrika Korps has:

"If a player passes, add two to his or her total (die roll)."