We are rolling out an RPG system for the fun of it. However, recent tests have lead us to a rather unsolvable problem.
In order to make single combat interesting and hopefully realistic, close-combat range was introduced. Essentially, every weapon covers one or several ranges, and fighting at an unsupported one is heavily penalized. That is, when they pass the tip of your spear, the combat is probably over for you(the spear covers only long range).
Now, the failing test setup. Ten guys are protecting the summit of a hill, while 20 others are storming it. One part of the attackers pinned down the defenders (short sword and large shield), while the two handed sword guys attacked from behind. According to the range rules, the defenders couldn't just turn around and stab the large sword guys and that was pretty important and interesting part of the combat.
The rule is definitely fun at single combat (1 vs 1). It is interesting and important for larger combat (30 participants), but as it is introducing a new state of the system, that has to be tracked, it bogs down combat immensely.
Now to justify the heading of my question, this problem is recurrent, when trying to design a system, that is meant to work on very different scales. For example, if our system gets to handle several thousand men fighting, there will definitely need to be a rule for morale and routing, because this is such an important variable in war. But morale checks would be utterly boring in heroic or single combat scenario.
How do we make the rule for close-combat range work? How do we phase it out in larger conflicts, as a plug-in to the rules, that is being disabled?