Editing RPG System Symmetries (section)

===Relative Size===
Systems should work the same if everything were shrunk or expanded uniformly. This should apply without having to change the absolute reference of the size scale. That is, if everything were shrunk by some percentage, you shouldn't have to redefine an inch just to make the system work. This doesn't mean that other absolute values related to size wouldn't change, but that all the rules still work the same just with the new stats. 

The distinction between the rules changing and the stats changing isn't entirely clear. Sometimes the rules may be consistant mechanically, yet fail logically. An example of this would be in GURPS (at least with RAW, there are official-unofficial addenda for a few of these). Two ants would have a large, negative size modifier, which would apply as a penalty on their chance to hit each other. This means that the two basically have no chance to hit each other. 

A more successful implementation of this symmetry can be found in the scaling rules from Mekton Zeta, and more fully realized in its advanced technical supplement, Mekton Zeta Plus. It presents a series of scales: Human (1/10 scale, for people and personal equipment), Roadstriker (1/5 scale, for Powersuits and small vehicles), Mekton (1/1 scale for most mecha, large vehicles, small structures), Corvette (10/1 huge mecha or vehicles, buildings, small ships), Starship (100/1 scale for capital ships, fortresses, and similar), and Excessive (no specific scale factor, reserved for relative comparisons among colossi such as the Death Star, the Midgard Serpent, Ego the Living Planet, the Zentraedi Base Station, or similar titans). Guidelines are also presented for defining custom scales, for example: 1/20 Pet scale, 1/100 Pest scale, or 1000/1 City scale could all be easily implemented.

Within the MZ+ scale framework, qualities such as height, weight, cost, range, and damage capacity all vary in one way or another with respect to scale, but things like to-hit rolls within a common scale are not effected. Only when differently scaled actors come into direct conflict do modifiers to action rolls appear. Off-scale components are also possible, such as a strike-fighter with anti-ship torpedoes or a battleship with anti-aircraft guns. The symmetry is not quite absolute, as special rules come in to play at Starship scale for crew actions and disabling ships' systems, and slightly different damage methods are used at Human scale for compatibility with other Interlock-system games (Cyberpunk 2020, et al).

I don't know of any system that fully exhibits this symmetry. Mekton Zeta largely succeeds, despite some inconsistencies and overlap potential here and there. GURPS tries, but in some places the asymmetries cause strange problems that require hand-waving on the part of the GM. In contrast, D&D has traditionally made only token efforts to be symmetrical with respect to size, giving rise to humorous situations where weasels or domestic cats may be more effective combatants than some low-level characters.