This idea gives attackers the opportunity to best use the surrounding terrain to their advantage, and to combine efforts in an attack.
There's opportunity for
attacks on a square to come from a direction - it would be set up in the same way that you'd set up a siege. This would allow the terrain from that direction to be used. Have a think through how the various combinations would work for or against various types of attackers and defenders.
We could also specify a divisional
direction for defence, but the proposition is a bit weaker for this idea. Maybe it's best used to align the army to cover weaknesses or strengthen a defence in an expected direction. Changes to stance are communicated by messenger, or improvised by a commander (where researched skills make them more adaptable)
Further, when
multiple armies try to prepare on a square (a process that should take a few minutes), there's opportunity for interaction. Allies/Confed will do something like a reinforcing Sally Forth, NAPs and will be a bit compromised, neutrals more so, and WAR will battle before any engagement with the target square. This 'preparation phase' allows coordination of armies from different players, letting the smaller players contribute effectively to a large attack, rather than simply going 'splat'.
Probably one for when Pathfinding™ happens.