Actually a combination would work best.

A wood log or stone or whatever shield on the opposite side of the fire perpendicular to the ground to reflect the radiant heat back towards the fire. And then the space blanket behind you at a 45 degree angle to reflect the heat down towards your body, presuming you're intending on sleeping. If you need the blanket to wrap yourself, as you suggested, then another perpendicular structure will suffice.

In a true survival situation I would block the wind. Even though it seemed to act as a fan to carry the heat towards you, it still robs your body of heat (wind chill), as well as burns your fuel faster.

BTW, I honestly haven't tried any of this personally, other than ad hoc wind breaks on campouts. But I think it will make an excellent weekend activity for our troop at the next campout!

Oh, we had three scouts build a survival shelter by leaning deadwood branches and leaves against a tree trunk at out December outing. They then spent the night in it with their sleeping bags and ground tarps/reflective pads under them. Temps were in upper 20's. The oldest was 14. The rest slept in the heated cabin!