The phrase "relative homogeneity" means that things are similar or alike in comparison to something else. It refers to a certain level of consistency or similarity within a particular group or context. Full definition
Data handling was better within this study with relative homogeneity of the treatment effects observed: of the six outcome measures used, only one parameter showed no effect of treatment (owner — directed aggression). (veterinaryevidence.org)
A reassessment of genetic diversity in Icelanders: Strong evidence from multiple loci for relative homogeneity caused by genetic drift. (decode.com)
Another thing you might notice in the more provincial places is the relative homogeneity of the researchers. (sciencemag.org)