ZOMBIEPOCALYPSE uses Hexagons that are six feet across. Why six-foot Hexagons? Well, partly because of my history playing Dungeons & Dragons ™ , which uses a similar grid, but largely because I wanted ZOMBIEPOCALYPSE to have a whole "number six" going for it. Six sided dice, six-sided hexagons, six feet across... it's all part of the pattern. But this left me with a bit of a conundrum.
Six-foot wide hexagons are huge. And the original rules stated that only one character (or Monster) at a time could be in any one Hex. Anyone trying to pass through an occupied Hex would find it impossible to do so, and the optional Attack of Opportunity rules meant that running away from a Monster in an adjacent Hex would give it a chance to hit you, even if it was potentially up to 12 feet away! That was just weird.
So I tweaked the rules (it's one of the advantages of being the author). Now I could have changed the size of each Hex, but that would have affected so many other rules that it wasn't worth it (plus, there was that whole "666" thing). Instead, I kept the Hexagons the same size but changed how many people can occupy one at the same time. Up to three characters - whether they are Player Characters or Monsters or a mix of the two) can occupy a single Hex at the same time. Creatures in the same Hex are considered within Melee range (creatures in adjacent Hex are also still considered in Melee range as well).
One bonus to this change is that it made explosive weaponry more effective; now weapons with Splash Damage - such as grenades - effect all the characters in a Hex. Some splash damage weapons also affect one to four surrounding Hexes as well; a large explosion (say, from an artillery shell) could now potentially kill up to 15 zombies (three in the targeted hex, plus three each in up to four adjacent Hex) with a single "To Hit" roll. This makes explosives far more deadly weapons. Of course, when I said they affect all targets, I meant all; any Player Characters or allied survivors can be hit by the blast as well. So use with care; GM's should be careful on how many explosive weapons they pass out, and Player Characters should take care in where they toss them.