The phenomenon you are describing is referred to as "calf ridge" and this ridge can interfere with your quilt sealing properly, and would explain the cold spot in your legs (your rear end is likely helping to seal the quilt which is why just your legs were cold). I defeated it by adding a huge draft tube on the leg end my UQ and playing around with a mini-spreader bar (which takes a lot of mods to work on a stock BB).