I set the nwwoodsman tarp-tent up again this afternoon and believe I got it setup the same as shown in the youtube video. It looked close and had that nice taut tarp sound when thumped.
The tarp is laid out on the ground with the longer dimention being the width and the shorter dimention being front to back. ie 12 ft wide and 9 ft front to back when laying flat on the ground.
At the back edge the 2 ground pegs are inserted at the loop 3 feet in from the corners. On the sides you go forward 6 feet to the loop on either side. Set the loop inward toward the center 3 feet on each side. This results in the forward pegs being directly forward of the 2 pegs at the back. These pegs essentially mark the corners of a 6 ft x 6 ft box.
Then the 2 poles are attached at the center ring at the peak which is when at ground level 3 feet further forward. Then when the 2 poles are raised the but end of the poles are moved a few feet toward the rear of the tarp. Thus the two poles not only angle in from the sides to the peak but also angle forward toward the peak too. The video I think makes it look like the poles come out at a 90 degree angle to the peak. But if that is done then lower down the poles will not be over or directly out from the side tie outs.
Anyway , with the tarp erected correctly - with the doors closed as shown in the video you enclose a floor space which is 6ft x 6 ft. The side pull outs , plus the rear pull out make the walls near to vertical so that most of the floor space is usable. Only the rear corners are not of much use.
The peak height on the inside , just below where the two poles cross over head measures 71 1/2 inches . So just a touch under 6 feet in height. But that height is only in one place and that is directly underneath the area reinforced for the ring which is tied to the poles crossing point. At the rear wall , just below where the ring is attached for the rear pull out , the height above ground is about 28 1/2 inches. Directly below that point measuring along the ground to the rear edge of the tarp measures about 24 inches, 2 ft.
Hope this answers the questions about the interior space of this size tarp set up as shown in the youtube video.
D