The Intermingled section is quite clear.
Quote:
Occasionally an attacker will wish to attack a position where units from two enemy formations are intermingled together. When a player declares the target for a charging formation he can choose, if he wishes, to include any enemy formations that are intermingled with the target formation as being part of the target of the charge. Two formations are intermingled if they have any units within 5cm of each other. If there are two or more formations within 5cm of the target formation, then the attacker can choose to include one or more of them as the target, he does not though have to include any of them.
An engage action is always targetted at a single enemy formation. Once the target formation is established, any other formations within 5cm of the target can be pulled into the fight. At that point, the intermingled formations become one formation.
Quote:
Once the move is complete, the engaging formation must have at least one unit within 15cms of a unit from the target formation. If this is not the case then the assault does not take place and the action ends.
Rules on making a Charge move.
So in the example in Dave's first post, if a player wishes to declare an intermingled engagement against A, B & C, Formation B has to be the initial target (assuming A and C are not within 5cm of each other).
Quote:
For the purposes of the assault, the intermingled formation is treated as being a single formation.
This part of the Special Rule really pertains to the actual mechanics of resolving the engagement rather than effecting the initial charge move.