I have a Yaris HB and purchased for the good storage as well. No lip at the hatch making it easy to slide big heavy objects in and out.
I typically get around 45 MPG with the worst case logged in at 37 MPG in the winter.
The COD as stated earlier is about 0.29 (for both cars?) is probably based on prototype measurements. I am certain there is a real difference, especially if different size tires, rim diameters, and body options are taken into account thought out the model line. Just as a side note, two different design teams worked on the Yaris. One for the LB and another for the sedan - this is likely the reason for the differing platforms.