The way I read it: when rolling doubles (and no exceptions apply) all units involved cower (the rules elsewhere also say, that the attack cowers; as said, I think that is not helpful). If it's just one unit, it is the one marked FFed of PFed. If there's more than one, RS determines which are marked. Regardless, since all units cowered, Fire Lanes are not placed. That's pretty logical to me.
A more reflective remark: I think that the reason for the RS is not meant to possibly 'save' Fire Lanes from being not-placed, but to prevent (as much as possible) a massive FG to be FF'ed all at once; i.e. in order to prevent one doubles die roll to hamstring a whole bunch of units at once.
A more reflective remark: I think that the reason for the RS is not meant to possibly 'save' Fire Lanes from being not-placed, but to prevent (as much as possible) a massive FG to be FF'ed all at once; i.e. in order to prevent one doubles die roll to hamstring a whole bunch of units at once.