I used two level 1 Chocobos as my COMs. Both had only Attack and Ruin for command abilities. One Chocobo was infused to have Chain Bonus Boost II (it also has some other passives that don't affect chaining. I can list them if you really want me to). I used MED/MED/Chocobo normal paradigms for the tests and fought a Ceratosaur encounter in Sunleth Waterscape 300 AF. Ceratosaurs have 0 chain resistance. They do have elemental weaknesses, so I'll use a RAV with only Blizzard for that test so that I don't introduce a new variable. The Chocobos only ever used Attack and Serah kept its HP in the green (mostly at full). Skip the preemptive strike.
Chain Bonuses: Chocobo without Chain Bonus Boost II: +0.5 per hit Chocobo with Chain Bonus Boost II: +2.5 per hit
I went with a level 1 Buccaboo Ace as my Rav monster for testing. The no Chain Bonus Boost II Buccaboo Ace only has Stagger Maintenance as a passive. I used MED/MED/Buccaboo Ace normal as my paradigm. Its only command ability is Blizzard. Since the base chain bonus of Blizzard is so high (and there is a Ravager bonus as well), I could only get a full chain bonus reading on the second Blizzard in each chain.
Chain Bonuses: Buccaboo Ace without Chain Bonus Boost II: +11 Buccaboo Ace with Chain Bonus Boost II: +13
In both cases, learning Chain Bonus Boost II increases the chain bonus of abilities used by 2 percentage points. You should be able to repeat this very easily.
Etro's Gate---The gameplay nexus for Fabula Nova Crystallis Final Fantasy http://etrosgate.com/