Where you have several units engaged in a single combat, you do not count the Rank Bonus for all of them. Instead, count only the Rank Bonus that grants the highest number of bonus combat result points.
For example, if you have two units engaging a single enemy unit in combat, one of which has a Rank Bonus of +1, the other of which has a Rank Bonus of +2, you may claim a bonus of +2 combat result points as that is the higher.