Go back through your study and evaluate the key nucleocapsid mutations between 200-207 (I think).  There was a recent study regarding mutations in this region which increased the viral rna packing per virion for one mutation versus the others. In layman’s terms, with identical exposure between two variants, the variants carrying the identified mutations increase the injection of viral load per virion- hence, the virions carry more bang per buck (like delta) with only a minor tweak of the nucleocapsid linker region. I want to say it was 100 fold increase if I remember correctly.