I feel strange siding with Elmer, but as I understand it, defect density shouldn't be different between SOI and bulk. It has to do with foreign matter (dust) not the kind of wafer--same fab, same air, same defect density. If there are problems peculiar to SOI, they would not be defect density.
Unless there are using bad wafers...
EDIT: Well, process size should matter, but they are both at 13nm here too.