Here's a link to an article some of us at the University of South Florida wrote on why latrine setback distances should not be considered a one-size-fits-all methodology.
iwaponline.com/washdev/article/13/10/833/97930
We know we aren't the first ones to understand this underlying problem, but, to our knowledge, we are the first ones to look at how these guidelines developed and what field papers they use as their reason for a given distance. We hope you find this information useful.