OS are larger, but (from what I have observed), mt tern is a ferocious beast. I haven't put anything in with the OS that wasn't meant as food, but I did judt try a pink tipped anemone wit the tern 2 days ago.
She immediately 'snuck up' on it and attacked fiercely.
I had 2 green chromis in with my G. Viridis (he's not even 3" long...) months ago, and he murdered one of them , for getting nosy at the base of his burrow. The other, i returned to the LFS.
Things that don't get killed in my (6) mantis tanks...
O,Scyllarus: For some reason, there is one snal that he just doesn't eat...other than that, whenever the top comes off, he knows ir's 'feedin' time'.
G. Ternatensis: She doesn't hassle a medium sized feather duster worm, the many copepods and amphipods and the 2 lettuce nudibranchs that I recently added for algae control (freebies from a LFS). Mushroom corals are left alone.
G. Platysoma: He left a peppermint alone for a bit,but eventually ate him. he doesn't seem to really care for snails, so the are relativeliy safe ( as mantis Shrimp tanks go...). He lives with zoos,mushrooms and I currently have a pink tipped anemone in there, but I am removing that tonight, so that it doesn't get attacked like the one i the Tern's tank did.
G. Chiraga: She hasn't injured the new colony of yellow polyps that I added 2 days back, and she seems to ignore hermits for the most part.
N. Wennerae: Not much in with him...he has left larger snails alone, but eats the little ones.
G. Viridis: Here's the strange case...This, my first mantis shrimp, has lived with several 'prey' items for months without attacking them.
An emerald mithrax, 5-7 hermits,...he eats snails, but has a few bigger ones that he leaves alone. He hasn't molested the lettuce nudi yet, either. His tank is filled with amphipods and copepods, so maybe he is eating them...as well as snails. As I said, he killed the green chromis that I added.
Not really an answer to your specific question, but perhaps it shed some light on aggressiveness.
-Ron