Sometimes, a charging unit will straddle two arcs. In such cases, count how many models in the front rank of the charging unit lie within each arc. If there are more models in one arc, the unit is considered to be in that arc.

If it is still unclear, the charging unit is considered to be in the arc that gives it the least advantage in terms of combat result. For example, if you cannot determine whether a charging unit is in the flank or rear arc, it is in the flank arc.