IMHO, size really matters in what you are trying to portray. I for the most part Campaign, however I use varying map sizes depending on the battle and its location. I use bigger maps for open spaces and smaller for the more closed in areas, but this is only a guideline so it can become fairly mixed up as well. I try to think of what my KG's mission is and where is it on the battlefield. I'm I, an armoured Recce in force, or a flank guard or a defending a sector with other units etc, all these factors figure into what your units' Area Of Responsibility (AOR) might be.
80 x 80 does seem to be a good generic size if that is more what you are looking for.
Bob out
