You're not out in the open you're in a bivy.
I recently ordered another Superlight. I wanted a 1.0 DCF bottom rather than the .75. Ron, the Chief Happiness Officer, said not doable.
He suggested a polycro ground sheet so...
I use a current Lg with a NEoAirXLite Shorty or Womans length inside teh Superlight and I'm 6'4" 205Lbs. I don't bring my gear inside though. I do wear apparel but not Michelin Man belaying type poofies.
Be glad you have the DCF bottom if you use a polycro ground cloth. With the silny bottom I slide all over with my tossing and turning. Putting the pad inside less overall sliding around. Trying to sleep with the pad outside the silny bottom bivy using poly I've almost slid off ledges unless it's really flat ground.