The other birds are standards.are your normal flock birds standard size? maybe it is just a case of being bullied away from the food.
The personality of a cochin my sister had, was very much go sit in the corner and let the other birds peck me all the time. even separated from the flock after that, she avoided the food and water for an extended period of time.
But these bantams are kept in their own tractor.
We have decided to go full blown cleanout with our barn.
We are building cattle panel hoops to go in the front yard to hold our layers and will move the bantams out front too.
With them out of the coop we will clean out our entire barn, spray it for mites and external parasites, treat the birds for cocci and bomb the barn with mouse poison to kill off the army of mice living there.
We are just going to try to clean the place out and get the nasties out of there.