Exodus 26:12

And the part that remains of the curtains of the tent , the half curtain that remains , shall hang over the back of the tabernacle .

As for the additional length of the tent curtains, the half curtain that is left over is to hang down at the rear of the tabernacle.

And the remnant that remaineth of the curtains of the tent, the half curtain that remaineth, shall hang over the backside of the tabernacle.