Formation

Formation is the starting position of your army in a fight/battle. The units are spread as evenly as possible from top to bottom without any blanks, regardless of how the units are arranged in your heroes unit bar (having units in spots 1,2,3 is the same as having them in 2,6,7)

There are 2 options for formation "loose" and "tight" and the option can be toggled on the hero screen.

As their names suggest this changes how the units are grouped on your side of the battle. Loose spreads the units out evenly from top to bottom. Where as "tight" will cluster them together at the center, leaving nothing at the top and bottom.

Loose has the advantage of spacing your units apart, making "splash" attacks from those dragons with breath attack or lich and their death cloud attack, and spells like fireball less likely to hit multiple units.

Tight has an advantage of grouping units tightly, and can help protect archers and ranged attackers.

When fighting Creature Banks, the hero's army will be arranged in a special way, forming a hexagon (or part of one) in the centre of the battlefield, while the defenders of the bank will be arranged around the outside. Tight/loose and tactics have no impact on the formation of your army when fighting a creature bank.