I have a campmor extended poncho (5x9)and decided to see if I could get it to set up into something between a half pyramid with a forrester type flap front with enough room to sit up in, bug tent etc.
It will work, but its just not quite long enough for me as I am 6'3. A factory poncho/tarp would setup into a 5'3x6' tent in this type configuration.
Worked at it and came up with this. You could extend a campmor 5x9 poncho 3' and have plety of room, IE 5'x12'. I almost broke the sewing machine out then I decided to just build one from scratch since its just on long piece of fabric with the beak attached
Adding the front beak adds more room and really a better setup with more rain coverage, but you could still use it as a flat tarp if you wanted to.
Used as a poncho shown below is 5'x12' so you would have a 3' section to fold under to use it as a poncho. No big deal really. I am tall with monkey arms so I think the beak would come down to one wrist.
To set up, Stake the back 12' side at 9', 18" flap corners go under the tarp, pull the front in square, so you end up with a 9'x5' square, 3'-6" high at the peak held up by a hiking pole.
If you were shorter you could make it 5x11, or 5'3x8' set up.
The forrester type front flapped over and closed would provide a lot more protection than making the beak fromt he original width. It could be staked more straight out for more air or more straight down for better protection.
It will work without the beak, but this should be more versatile for 1.75 oz.
The 3D model is shown with another idea. Take a couple of pieces of tyvek and make doors. Just velcro or zip them under the forrester type flap.
Just the fabric for that would weigh 2.5 oz. If you made a bug tent with a silnylon or tyvek door on that side you would not need it.
I figure without the door it should weigh about 13 oz for just the tarp.
You would want to guy out the center of each side for a little more room.
This is the plan unfolded, plan looking at the top, set up, and the front view. The dashed lines are the fold lines. I have some spare tyvek so maybe I will build a test model first.