Once free to move in a hammock w top quilt
I lost interest in expanding the bag. I see that Western Mountaineering recognizes that some would their mummy bags be larger, so a couple of their models are larger twins of previous ones.
Related to this thread is my TQ for a chilly but rarely freezing November in Oregon. I opened the back of one of the RAB top bags that was discussed here -- a sleeping bag with just fabric on the bottom except for a fully enclosed and insulated foot box. Expectation is that the user would like in a pad and his body. Or just his body, and then lay on a pad. I, instead, slit and sealed the fabric to just below the neck, leaving an intact collar. I can then step into the footbox, pull the collar around my neck, to keep the the bag / quilt over me, and yet have freedom of movement between and neck and knees.