It would be nice also that the artificial reference represented global population structure- for example, the larger the genetic distance between an individual who is sequenced, and the identity of the person who makes up the reference (an amalgam of several individuals from a common US population), the less compression you get. Instead, it seems like you could create the "genome that is the shortest distance to all other genomes" (a centroid of cluster centroids) and then the standard deviation of your compressed sizes should be much smaller.