I use a slightly larger than normal poncho (about 5.75 X 8.5 feet) as both rain gear and shelter. Depending on the site and the weather I expect, I use one of three pitches (using my hiking poles).
My preferred use is as a lean-to or "Baker-pitch": just a line from the centre of the short side of the poncho on each end, over my poles and to a stake. Then a line from the front edge at each end down to the ground. Then short lines from the two back corners to the ground. Usually I leave a couple of inches from poncho to ground in back. I have the lines made up and packed so I can do this in a couple of minutes. Just be careful with the direction you pitch, and don't trip over the front lines.
In really nasty weather, I do it pup tent style, over my poles and pinned tight to the ground. I generally have to pull one of the front stakes to get in, and it's a nuisance, but it's warm and dry, and won't blow away or collapse. I do use a line at each end from peak to ground. Condensation can be as bad as the rain. I use a very light bivy.
For sorta ordinary rain (especially if I'm wearing the poncho) I like to set it up in a pyramid against one pole. This is very easy and quick, it gives you a bit of headroom, it's pretty much fully enclosed, and, with some practice, it can be done from inside the poncho, so you don't get wet while you're doing it.
Just peg ties about a third in from each end of the long side (I use short lines that gives me a couple of inches of space between the ground and the fabric). Run a line from the centre of the opposite long side to your pole and then to a stake (gotta go outside to do this). Then bring the two ends around to the front and peg them. It's one of those things that's easier (and faster) to do than to describe. Problem with this one is that if it chills before morning you'll usually get some condensation. I've had a couple times I was glad my sleeping bag was in a bivy.
Sorry, no pix at this time (even thou that was my business).
I generally just use an A frame. The 8X 10 is great and provides plenty of rain protection in that setup, especially if you are solo. However, that trapezoid under a tree looks pretty good. I have sat in a lot of rain storms in the rockies under a big pine and have been dry the whole time. The tree itself keeps a lot of water from hitting you. Putting the tarp up against the tree with make it even better, and still maintain good condensation control. I need to try it out.
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