p225, "each element may normally make one attack...attack declaration must include the attacking Element, its target..valid targets are other Elements.." Ie. Each Element makes it's own attack and it targets an attack at a specific element ('mech, tank), not a unit (lance).
There's nothing about a unit (lance) having to attack the same target, and it even says an element capable of multiple attacks may attack different targets, so the unit (lance) overall can't be limited to one target.