The way the Speer is shaped, smaller radius on the inside next to the hammock and larger radius outside is what seems to me to be the big advantage. But if those of us who have a JRB Nest, for instance, would shorten the length of the material that makes up the breadth of the undercover on the inside only, then the quilt would pull up to you in the hammock and would stop before the longer, larger radius on the unaltered outside of the quilt could compress the down.
The JRBs seem to have the same width on both the inside and outside. The Speers hugger seems to be narrower on the inside and wider on the outside dimensionally.
Does this make sense?