IMO cories really don't bother shrimp, healthy ones at least. I have kept full grown green aeneus in my shrimp tanks before and not noticed any trouble as far as population growth in the shrimp colony. Well fed cories are lazy. Fact. The last thing they want to do is try to catch up with a healthy tiny shrimplet.
I've even seen my school of cories sharing bottom wafers with shrimps of all sizes without issue.