I'd use swede for a quick boil, or to light the Siberian. If I needed a warming fire for the supershelter, I'd "aim" the Siberian at the clear, vertical side of the plastic lean-to. The raised wooden bed lets the radiant heat pass thru the two layers of clear PEVA shower curtain (assembled to a reflective tarp to make the 12x12) get under you and allows room to put head-sizes hot rocks in pits under the bed, too. There's several quick, easy ways to make a raised wooden bed. Stack logs between 4 stakes to make a wall, drive 4 corner stakes, with forked ends or notch them for the cross logs, etc.
You can either use the remainder of the reflective tarp as a poncho and leggings or as a reflector on the far side of the fire. In my experience, the clothing keeps you warmer than any reflector. You should, however, have a log and tarp wind block around and above the Siberian, so that smoke is drawn to that rather than to your shelter and to keep down wind gusts that might blow embers onto your shelter. Another reason to take the big roll of duct tape, repairs! :-) The Siberian is just as warm at 6 ft as a regular fire is at 3 ft, making it much less likely that you'll burn holes in your clear PEVA