walled/defensive formation question

[Bullets_inc]

when defending sometimes my troops spread out along city walls and defend using the defensive structures other times the stay in formation and keep getting flanked as if i had issued a halt command.  Is there a key command to order units to disperse and use defensive structure such as walls when they are in a defended flag zone such as ammo dump?  thanks for your help

[Henry d'Esterre Darby]

You can select the unit, then right click the icon on the field for the defensive position to tell the unit to man that that position.  The icon is usually a silver shield.