Lets look at what we can represent with the infantry of a four-stand French division. The idea is to represent the posture and intent of the formation by the position of the stands. If the rules work properly, transitions between states and the movement of the stands should be natural. In an ideal world, perhaps formation rules are not really needed -- instead, the interaction of the individual stands with each other and with enemy stands should drive out the desired effects.
Anyway. This infantry division is concentrated. It should be able to move handily and respond to threats from all directions, but should be vulnerable to fire and reasonably easy to see. I suppose it can be thought of as battalions marching in parallel in columns of company.
This infantry division has extended a firing line but is supporting it with a solid reserve. If the reserve is in cover (say behind a ridge line) the units in the firing line would be refreshed with rotation of new units. The reserve would also permit the division to respond to threats from the flank or rear.
This infantry division has committed itself completely to the firing line. It has maximum firepower in the defense, or the greatest power to find and encircle enemy flanks in the attack, but it cannot easily reply to flank threats.