It certainly does Ludwig, I remember one time my sister and I caught a heap of local creek shrimp as live food for my sisters Oscars, and rather then letting all the shrimp into the Oscar tank at once to just be killed and wasted we put most of the shrimp in another tank housing neon tetras. Within a very short spate of time we could see the macrobachium species of shrimp actively hunting and grabbing the tetras and eating them.
There could be something in the chunky and slim theory with these shrimp. Perhaps the chunky ones are female and like female mosquito's need a protein rich diet in order to breed.
And I also give my shrimp defrosted bloodworms they absolutely adore them, so maybe some of my "potential" fish eaters ( I don't have amano but I do have typus and other species of shrimp that could take a liking to eating fish), are getting the protein they crave, thus leaving my fish alone.