If just your hip is cold, check to see if you are hanging the underquilt too tight. With the hip being the lowest point, if the underquilt is too tight it will compress the insulation. Making a cold spot. It might be hang too loose. But I think that would cause more cold spots.
Is that too much to ask? Girls with frikkin' lasers on their heads?
The hanger formly known as "hammock engineer".