How do you make cases comparable when using the middle range approach?

Beaulieu Scharnhorst & Wouters examine the the questions of science and technology studies and examine the methods for selecting to use case studies to answer these questions.  Using their own work they examine why and how they use cases to reflexively portray "the institutional and cultural context" that case studies are used to create knowledge.  Doing so allows them to provide benefits of using cases studies as well as elaborate on new ways of using case studies.

They advocate a middle range approach by using various methods, concepts and empirical work and elaborate on what that might look like in practice focusing on the use of ethnographic case studies.  The authors argue that using reflexivity in the form of an ethnographic approach allows researchers to "make sense of success and failures".  They also challenge a one size fits all knowledge making practice because they use ethnography and historical scholarship to produce knowledge in their own research of e-science.  Through reflexivity they identify that "a unit for comparison has to be constituted, and features for comparison have to be specified, if [a middle range approach] is to yield interesting insights" (677).  To me personally this seems difficult to do since there is no unification between research method approaches in "women's studies", "molecular biology" and "high energy physics" and how does one develop a unit for comparison? This they argue is a major middle range issue-what counts a proper comparison-and how does one make a case comparable?